System and method for an inverter for self-excitation of an induction machine

ABSTRACT

A capacitor is connected between the direct current voltage terminals. Switched terminals of a first switch and a second switch are coupled in series, between the direct current voltage terminals. An electric machine or generator has one or more windings and a first phase output terminal associated with the switched terminals. A first set of blocking diodes are cascaded in series and second set of blocking diodes are cascaded in series. A first voltage supply provides a first output voltage level and a second output level switchable to the first control terminal, where the first output level is distinct from the second output level. A second voltage supply provides the first output voltage level and the second output level switchable to the second control terminal.

RELATED APPLICATION

This document (including the drawings) claims priority based on U.S.provisional application Ser. No. 62/346,114, filed on Jun. 6, 2016 under35 U.S.C. 119(e), which is hereby incorporated by reference into thisdocument.

FIELD

This disclosure relates to a system and method for a self-exciting of aninduction machine, and more particularly for a self-exciting aninduction generator (e.g., three-phase, squirrel-cage inductionmachine).

BACKGROUND

In certain prior art, the windings of an induction generator can beexcited by various schemes. Under a first scheme, a battery is connectedacross the direct current bus of an inverter to excite one or morewindings of an induction generator. Under a second scheme, a bank ofcapacitors is connected to one or more windings of the phases of theinduction generator to excite one or more windings of the inductiongenerator. However, both the first scheme and the second scheme requireadditional components beyond the driver circuit for the inverterswitches. Further, a bank of capacitors can increase the volume, sizeand/or weight of an inverter and induction generator. Any unnecessaryincrease in the weight of the inverter and induction generator tends toreduce fuel efficiency of a vehicle that incorporates the inverter. Forthe above reasons, there is a need for an improved system and method foran inverter for self-excitation of an induction machine.

SUMMARY

In accordance with one embodiment, an inverter system comprises a pairof direct current voltage terminals of opposite polarity. A capacitor isconnected between the direct current voltage terminals. A first switchhas first switched terminals and a first control terminal. A secondswitch has second switched terminals and a second control terminal. Theswitched terminals of the first switch and the second switch are coupledin series, between the direct current voltage terminals. An electricmachine or generator has one or more windings and a first phase outputterminal associated with the switched terminals between the first switchand the second switch. A first set of blocking diodes are cascaded inseries and second set of blocking diodes are cascaded in series. A firstvoltage supply provides a first output voltage level and a second outputlevel switchable to the first control terminal, where the first outputlevel is distinct from the second output level. A second voltage supplyprovides the first output voltage level and the second output levelswitchable to the second control terminal.

In a start-up mode, a power supply provides the first output level orelectrical energy via the first set of blocking diodes and the secondset of blocking diodes to the capacitor to charge (e.g., trickle charge)the capacitor to enable self-excitation of alternating current flux inone or more windings associated with the first phase output terminal.The charged capacitor provides initial electrical energy to overcomelosses in the induction machine, the inverter and conductors (e.g.,cable) such that (e.g., in a transitional excitation mode) when therotor of the induction machine is rotated by a source of rotationalenergy, in the transitional excitation mode the induction machine canself-excite or induce a sustained alternating current in one or morestator windings of the induction machine; where the inverter can convertthe alternating current into a suitable direct current voltage (e.g.,high voltage) on the direct current voltage terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one embodiment of a schematic representation of a first phaseof an inverter and an associated driver for a self-exciting of aninduction machine.

FIG. 2, which is collectively FIG. 2A and FIG. 2B, is one embodiment ofa schematic representation of an inverter system with three phases thatare connected to an induction machine or generator, where the invertersystem is arranged to self-excite an induction machine. FIG. 3A isanother embodiment of a schematic representation of an inverter systemthat is connected to an induction generator, an active load thatcomprises a secondary inverter and an electric motor, and a passive loadthat comprises a switched resistive load.

FIG. 3B is another embodiment of a schematic representation of aninverter system that is connected to an induction generator, an activeload that comprises a secondary inverter and an electric motor, and abattery, which can act as a passive load when discharged.

FIG. 4 is yet another embodiment of a schematic representation of aninverter system that is connected to an induction generator, an activeload that comprises a secondary inverter and an electric motor.

FIG. 5A is a block diagram that illustrates one possible embodiment ofthe modules (e.g., software) associated with the driver or controllerfor the driver.

FIG. 5B is a block diagram that one possible embodiment of the logic ormodules (e.g., software) for controlling a mode of operation of aninverter.

FIG. 6A is an illustrative chart that represents one possible waveformin the ramping up of the excitation voltage in the capacitor versus timeduring the start-up mode, transitional excitation mode and reaching orapproaching full target excitation voltage in the operational mode,among other things.

FIG. 6B is an illustrative chart that represents another possiblewaveform in the ramping up of the excitation voltage in the capacitorversus time during the start-up mode, transitional excitation mode andreaching or approaching full target excitation voltage in theoperational mode, among other things.

FIG. 7 is a block diagram that illustrates one possible configuration ofthe driver controller, the driver, the inverter, the induction machineand the prime mover, such as an internal combustion engine.

FIG. 8 is one embodiment of a flow chart of a method for a self-excitingof an induction machine.

FIG. 9 is another embodiment of a flow chart of a method for aself-exciting of an induction machine.

DETAILED DESCRIPTION

FIG. 1 is one embodiment of a schematic representation of a single phaseor first phase of an inverter system 11 and an associated first phasedriver 18. In accordance with one embodiment, an inverter system 11comprises a pair of direct current voltage terminals (28, 30) (e.g.,direct current voltage bus) of opposite polarity. A capacitor 26(C_(DC)) is connected between the direct current voltage terminals (28,30). Each phase of the inverter includes a pair of switches, such as afirst switch 12 (A₁) and a second switch 14 (A₂). A first switch 12 (A₁)has first switched terminals 54 and a first control terminal 50. Asecond switch 14 (A₂) has second switched terminals 56 and a secondcontrol terminal 52. The switched terminals (54, 56) of the first switch12 and the second switch 14 are coupled in series, at the first phaseoutput terminal 53, between the direct current voltage terminals (28,30) (e.g., DC+ and DC− terminals in FIG. 1). In this document, thedirect current voltage terminals (28, 30) shall be synonymous with thedirect current bus.

In one embodiment, if the first switch 12 comprises a transistor, suchas a bipolar junction transistor or insulated gate bipolar junctiontransistor (IGBT), the first switched terminals 54 comprise an emitterand a collector. The first control terminal 50 of the first switch 12may comprise a gate or a base of the first switch 12. In one embodiment,if the first switch 12 comprises a field-effect transistor, the firstswitched terminals 54 comprise a source and a drain. The first controlterminal 50 of the first switch 12 may comprise a gate or a base.

Similarly, in one embodiment, if the second switch 14 comprises atransistor, such as a bipolar junction transistor or an insulated gatebipolar junction transistor (IGBT), the second switched terminals 56comprise an emitter and a collector. The second control terminal 52 ofthe second switch 14 may comprise a gate or a base of the second switch14. In one embodiment, if the second switch 14 comprises a field-effecttransistor, the second switched terminals 56 comprise a source and adrain. The second control terminal 52 of the second switch 14 maycomprise a gate or a base of the second switch 14.

A protection diode or free-wheeling diode (13, 15) may be connectedbetween the switched terminals (54, 56) of each switch to protect theswitch from transient currents that occur during switching transitionsof the first switch 12 and the second switch 14. For example, the firstprotection diode 13 may conduct to dissipate transient energy associatedwith an electrical energy spike when the first switch 12 is switched offand the inductive motor winding, motor or induction machine 55 inducesthe energy spike. Similarly, the second protection diode 15 may conductto dissipate transient energy associated with an electrical energy spikewhen the second switch 14 is switched off and the inductive motorwinding or motor induces the energy spike.

An electric machine 55 (in FIG. 2) or generator has one or more windings(57, 157, 257 in FIG. 2). With respect to FIG. 1, a first phase outputterminal 53 is associated with the switched terminals (54, 56) betweenthe first switch 12 and the second switch 14 and the first phase output53 terminal can be coupled or connected to a winding (e.g., phasewinding) of the electric machine 55.

A first phase driver 18 (e.g., first driver) comprises a first powersupply 22 and a second power supply 24 that are controlled by, modulatedby, or switched by a driver controller or an electronic data processingsystem 100 (e.g., that uses the control switches (S1, S2, S3 and S4). Inone embodiment, the first power supply 22 comprises a first voltagesource 38 and a second voltage source 40. In another embodiment, thesecond power supply 24 comprises a first voltage source 38 and a secondvoltage source 40. In certain embodiments, neither the first powersupply 22, nor the second power supply 24 is capable of providing enoughcurrent to establish directly the requisite electromagnetic flux oradequate excitation in the induction machine 55, such that in a start-upmode a trickle charging technique is used to establish theelectromagnetic flux or adequate excitation in the induction machine 55for entry into the transitional excitation mode. The trickle chargerefers to a slow or gradual charging over time of the direct currentcapacitor 26 or the direct current bus at a lower current level than athreshold current level, such as the threshold current necessary toestablish to establish immediately and directly the electromagnetic fluxor adequate target excitation voltage in the induction machine 55 (e.g.,that would be characteristic of an operational mode). That is, thetrickle charge prepares the inverter system 11 for entry into thetransitional excitation mode as an intermediate preparation for theoperational mode. For example, the stored energy (E) in joules in aplanar, parallel plate capacitor can be modeled as equal to ½ CV², whereC is the capacitance in Farads and V is the voltage in volts.

In one embodiment, the first phase driver 18 comprises a first biasingnetwork 33; the first biasing network 33 comprises a first set ofblocking diodes 32 are cascaded in series between one of the directcurrent terminals (28) and a node 37 associated with the first powersupply 22 and a first control switch 42 of the first phase driver 18. Inone embodiment, the first phase driver 18 comprises a second biasingnetwork 35; the second biasing network 35 comprises a second set ofblocking diodes 34 that are cascaded in series between the first phaseoutput terminal 53 and a node 39 associated with the second power supply24 and a third control switch 46 of the first phase driver 18.

In one configuration, a first power supply 22 provides a first outputvoltage level (e.g., positive 15 volts direct current (VDC)) and asecond output level (e.g., negative 8 volts direct current (VDC))switchable (via control switches (42, 44)) to the first control terminal50, where the first output level is distinct from the second outputlevel. Similarly, a second power supply 24 provides the first outputvoltage level and the second output level switchable (via controlswitches (46, 48)) to the second control terminal 52.

In one embodiment, the first power supply 22 is associated with a firstcontrol switch 42 (S₁) between the first control terminal 50 and thefirst output voltage level at node 37; the first power supply 22 isassociated with a second control switch 44 (S₂) between the firstcontrol terminal 50 and a node at the second output level. One or moreresistors may be associated with the first control terminal 50. Forexample, a first input resistor 20 (e.g., gate resistor, R_(G1)) iscoupled between the first control terminal 50 and a terminal of thefirst control switch 42, and a second input resistor 21 (e.g., gateresistor, R_(G2)) is coupled between the first control terminal 50 and aterminal of the second control switch 44. In practice, the secondcontrol switch 44 can be turned on to hold or bias (e.g., by maintaininga negative gate-to-source voltage or appropriate bias voltage asrequired based upon the semiconductor configuration or doping of thefirst switch) the first switch 12 in an off mode.

Similarly, the second power supply 24 is associated with a third controlswitch 46 (S₃) between the second control terminal 52 and the firstoutput voltage level at node 39 and a fourth control switch 48 (S₄)between the second control terminal 52 and a node at the second outputlevel. One or more resistors may be associated with the second controlterminal 52. For example, a first input resistor 20 (e.g., gateresistor, R_(G1)) is coupled between the second control terminal 52 anda terminal of the third control switch 46, and a second input resistor21 (e.g., gate resistor, R_(G2)) is coupled between the second controlterminal 52 and a terminal of the fourth control switch 48.

FIG. 6A and FIG. 6B show illustrative examples of waveforms in theramping up or increasing of the excitation direct current voltage in thecapacitor (e.g., 26) versus time (or across the DC bus terminals (28,30)) during the start-up mode and the transitional excitation mode. Thedirect current voltage in the capacitor (e.g., 26) reaches or approachesfull target excitation voltage in the operational mode.

As used in this document, a start-up mode (e.g., weak pre-charge mode)shall mean a mode in which there is no switching (permitted) of theinverter switches (e.g., 12, 14 in FIG. 1 or 12, 14, 112, 114, 212, 214in FIG. 2) and the capacitor is charging or charged (e.g., tricklecharged) to an initial start-up voltage (level), a preliminary voltage,initial voltage level or an energy level that is: (1) sufficient toenable the inverter switches (e.g., 12, 14 in FIG. 1 or 12, 14, 112,114, 212, 214 in FIG. 2) to begin to operate, (2) greater than or equalto a minimum operational threshold direct current (DC) voltage, (3)supportive of a transitional excitation mode to increase or ramp up thedirect current bus voltage from the initial start-up voltage to a targetdirect current operational voltage or in accordance with self-excitationof the induction machine (e.g., 55) by the electromagnetic fieldsinduced by the moving rotor of the induction machine (e.g., 55). Forinstance, the rotor of the induction machine 55 may be moved byrotational energy applied from an internal combustion engine, a windturbine, a hydroelectric turbine, a wind rotor blade, a vehicle wheel,or another rotational energy source to induce or self-excite electricalenergy in one or more windings of the induction machine 55.

A transitional excitation mode can occur in a time period after thestart-up mode and prior to the operational mode. The transitionalexcitation mode is mode in which switching of the inverter switches(e.g., 12, 14 in FIG. 1) can occur (e.g., consistent with increase inthe direct current voltage). In practice, the transitional excitationmode between the minimum operational threshold direct current voltageand the target operational threshold direct current voltage may becharacterized by one or more generally linear slopes, or curved slopes,that increase from the minimum operational threshold direct current tothe target operational threshold direct current voltage.

An operational mode shall mean a generating mode in which the inductionmachine or induction generator can or is generating electrical energy inresponse to the application of rotational energy from a rotationalenergy source.

A transitional excitation mode shall mean one or more of the following:(1) a mode in a time window that occurs after the start-up mode andprior the operational mode, or (2) a mode after the start-up mode andduring an initial time period of the operational mode while thealternating current, or associated voltage output, produced by theinduction machine in a generating mode is increasing or ramping up to atarget operating voltage output (e.g., root mean squared voltage outputor DC link voltage). The target operating voltage output may be observedat the direct current terminals of the inverter that is coupled to theinduction machine to convert the alternating current output of theinduction machine to a direct current output in the generating mode. Inone embodiment, the self-excitation process (e.g., in which theinduction machine generates sustainable electrical energy to overcomelosses in the induction machine and inverter) occurs during thetransitional excitation mode, which is prior to or during theoperational mode. For example, the transitional excitation mode includesa time period, between the minimum operational threshold direct currentvoltage and the target operational threshold direct current voltage,when the inverter switches can operate (e.g., at less than peakalternating current output voltage) based solely on excitation followingthe start-up mode.

In a start-up mode (e.g., prior to the transitional excitation mode orself-excitation process), the first power supply 22 and the second powersupply 24 simultaneously each provide electrical energy at the firstvoltage level (e.g., approximately positive 15 volts direct current(VDC)) in series via the first set of blocking diodes 32 and the secondset of blocking diodes 34 to the capacitor 26 (C_(DC)) to trickle chargethe capacitor 26 to initiate the self-excitation of alternating currentflux in one or more windings (e.g., of the induction machine 55)associated with the first phase output terminal 53. Collectively, thevoltage applied to trickle charge the capacitor 26 is approximatelytwice the first voltage level, less voltage drops in the forward biaseddiodes of the first set of blocking diodes 32 and the second set ofblocking diodes 34 and less voltage drop in any resistors 36.

In an operational mode (e.g., or in the transitional excitation mode)after charging the capacitor 26, the power supply (22, 24) applies thefirst output level to the activate the first switch 12 or the secondswitch 14, whereas the power supply (22, 24) applies the second level todeactivate the first switch 12 or the second switch 14 in accordancewith a modulation commands (e.g., pulse width modulation commands orspace vector pulse width modulation commands) of the driver controlleror electronic data processing system 100. After the start-up mode andduring the transitional excitation mode, the first set and second set ofblocking diodes (32, 34) are reverse-biased so that the power suppliesdo not contribute to charging during the transitional excitation mode,where the increase in the direct current voltage is based solely on theelectromagnetic fields generated or induced by the rotor moving in theelectrical machine.

Collectively, the start-up mode and the transitional excitation modeshall be referred to as the self-excitation stage or start-up stage. Theself-excitation stage or the start-up stage is not entirely synonymouswith the start-up mode because the self-excitation stage includes boththe start-up mode and the transitional excitation mode.

In one embodiment, the induction machine 55 may comprise an inductiongenerator or an induction machine, such as a three-phase, squirrel-cageinduction machine (SCIM).

The start-up mode (e.g., the weak pre-charge mode) and the operationalmode are mutually exclusive and do not occur simultaneously. Forexample, a transition can occur (e.g., in a transitional excitationmode) between the start-up mode (e.g., weak pre-charge mode) and theoperational mode when the charge stored by the capacitor 26 issufficient to excite or self-excite one or more windings of theinduction generator (e.g., 55), which is capable of producing highvoltage electrical energy (e.g., 200 volts direct current or greater) onthe direct current terminals (28, 30) during an operational mode. Duringthe transitional excitation mode or during an initial time period of theoperational mode, the high voltage electrical energy is ramped up from astart-up voltage between the direct current terminals (28, 30) during astart-up mode. During the transitional excitation mode, it can bepremature to introduce a load (e.g., switchable load) to the directcurrent terminals (28, 30) prior to completion of the voltage ramp-up onthe direct current terminals because a premature introduction of a loadon the direct current bus can interfere with adequate energy storage inthe capacitor 26 for a sustained ramp up to a target output voltage onthe direct current terminals.

In one configuration, the first control switch 42 (S₁) and the thirdcontrol switch 46 (S₃) are off, or inactive, during the start-up mode,whereas the second control switch 44 (S₂) and the fourth control switch48 (S₄) are on or active during the start-up mode to deactivate thefirst switch 12 (A₁) and the second switch 14 (A₂). To control the firstswitch 12 and the second switch 14, the first control switch 42 and thethird control switch 46, respectively, alternate between off and onduring an operational mode in accordance with modulation commands (e.g.,pulse-width modulation (PWM)) from a controller after self-excitation ofthe (rotating) magnetic and electrical fields from the direct currentprovided by the capacitor 26 in one or more (stator) windings associatedof the induction machine (e.g. induction generator) with the first phaseoutput terminal 53.

In one embodiment, the induction machine 55 or generator comprises aninduction machine without any energy storage device connected betweenthe direct current voltage terminals (28, 30), except for the capacitor26, and without any capacitor connected to the first phase outputterminal 53 or any other phase output terminal (153, 253) theircorresponding alternating current terminals of the induction machine. Incertain embodiments, the induction machine 55 does not include anypermanent magnets in or for the rotor windings, the stator windings, orboth.

Before the self-excitation scheme has been initialized and during thestart-up mode, the first set of diodes 32 (D₁) and the second set ofdiodes 34 (D₂) and are forward biased and charge the direct current bus(28, 30) to a primary voltage or start-up voltage, such as approximately20 volts direct current (VDC) or greater (e.g., at the end of the firsttime period, T₁ in FIG. 6B). During the transitional excitation mode(e.g., after self-excitation scheme is initialized) or during theoperational mode of the induction machine 55, the first set of diodes 32and the second set of diodes 34 become reverse biased as the voltagebetween the direct current terminals (28, 30) rises, increases, or rampsup to a final, peak or steady-state secondary voltage (e.g. secondaryvoltage level or high voltage of approximately 200 volts direct currentor greater). During the transitional excitation mode or operationalmode, the reverse bias of the first set of diodes 32 and the second setof diodes 34 results from the alternating current induced in the firstphase winding 57 (e.g., Phase A) of the induction generator or inductionmachine 55 as the induction generator converts mechanical rotationalenergy into electrical energy. The reverse bias of the diodes (32, 34)ends the trickle charging of the direct current capacitor 26.

The final, peak or steady-state secondary voltage across the directcurrent bus terminals may comprise the target operational direct currentvoltage at the end of the third time period, T₃, or during the fourthtime period, T₄, in FIG. 6B. In one embodiment, the secondary voltageequals the start-up voltage plus a transitional voltage that ramps up orchanges over time before reaching the final, peak, steady-statesecondary voltage, or the target operational direct current voltage. Forexample, the secondary voltage may ramp up from approximately 20 voltsdirect current (VDC) to approximately 200 volts direct current orgreater, where the primary voltage as approximately 20 volts directcurrent. During the transitional excitation mode or operational mode,the reverse bias of the first set of diodes 32 and the second set ofdiodes 34 results from the alternating current induced in the firstphase winding 57 (e.g., Phase A) of the induction generator or inductionmachine 55 as the induction generator converts mechanical rotationalenergy into electrical energy.

Before the self-excitation scheme is initialized, the first switch 12(A₁) and the second switch 14 (A₂) are turned off in the start-up mode.During the operational mode, once the self-excitation scheme isinitialized the driver controller (e.g., first phase driver 18) orelectronic data processing system 100 controls the switching states (onor off states) of the first switch 12 and the second switch 14 inaccordance with a control scheme. For example, the second control switch44 and the fourth control switch 48 are on during the start-up mode tokeep the first switch 12 and the second switch 14 off during thestart-up mode. However, during the operational mode, the first controlswitch 42 and the second control switch 44 alternate between on and off;the third control switch 46 and the fourth control switch 48 alternatebetween on and off, such as in accordance with modulation commands(e.g., pulse width modulation or space-vector pulse width modulation) bythe first phase driver 18.

In one embodiment, the first output voltage level (e.g., +15 VDC) isgreater than the second output voltage level (e.g., −8 VDC), and thecapacitor 26 is charged to the primary voltage (e.g., primary voltagelevel) of approximately twice the first voltage level, less a firstvoltage drop associated with the first set of diodes 32 and a firstresistor 36 in series with the first set of diodes 32 and less a secondvoltage drop associated with the second set of diodes 34 and a secondresistor 36 in series with the second set of diodes 34. Although thefirst resistor and the second resistor may comprise a one kilo-ohmresistor, any other suitable resistance may be used to set, limit ormanage the level of the electrical current that trickle charges thecapacitor 26.

FIG. 2 is one embodiment of a schematic representation of an invertersystem 111 with three-phases that are connected to an induction machine55 or generator, where the inverter system 111 comprises one or moredrivers (18, 118, 218). The inverter system 111 of FIG. 2 is similar tothe inverter system 11 of FIG. 1 except the system 111 of FIG. 2 hasthree-phases of switches and drivers, whereas the inverter system 11 ofFIG. 1 only has a single phase of switches and drivers. Further, thesystem of FIG. 2 illustrates the connection or coupling of an inductionmachine 55 or induction generator to the inverter system. Like referencenumbers in FIG. 1 and FIG. 2 indicate like elements or features.

The first phase (or phase A) of FIG. 2 is identical to the descriptionof the inverter system of FIG. 1. The second phase (Phase B) and thethird phase (Phase C) are similar to the first phase (Phase A), excepteach phase is associated with an output terminal (53, 153, 253) with analternating current signal (e.g., generally sinusoidal waveform) with adifferent phase than the other alternating current signals of the otherphases.

In FIG. 2, the second phase of FIG. 2 comprises a third switch 112having third switched terminals 154 and a third control terminal 150. Afourth switch 114 has fourth switched terminals 156 and a fourth controlterminal 152. The switched terminals (154, 156) of the third switch 112and the fourth switch 114 are coupled in series between the directcurrent voltage terminals (28, 30).

In one embodiment, if the third switch 112 comprises a transistor, suchas a bipolar junction transistor or an IGBT, the third switchedterminals 154 comprise an emitter and a collector. The third controlterminal 150 of the third switch 112 may comprise a gate or a base ofthe third switch 112. In one embodiment, if the third switch 112comprises a field-effect transistor, the third switched terminals 154comprise a source and a drain. The third control terminal 150 of thethird switch 112 may comprise a gate or a base.

Similarly, in one embodiment, if the fourth switch 114 comprises atransistor, such as a bipolar junction transistor or an IGBT, the fourthswitched terminals 156 comprise an emitter and a collector. The fourthcontrol terminal 152 of the fourth switch 114 may comprise a gate or abase of the fourth switch 114. In one embodiment, if the fourth switch114 comprises a field-effect transistor, the fourth switched 156terminals comprise a source and a drain. The fourth control terminal 152of the fourth switch 114 may comprise a gate or a base of the fourthswitch 114.

In the second phase, a protection diode or free-wheeling diode (113,115) may be connected between the switched terminals of each switch(112, 114) to protect the switch from transient currents that occurduring switching transitions of the third switch 112 and the fourthswitch 114. For example, the third protection diode 113 may conduct todissipate transient energy associated with an electrical energy spikewhen the third switch 112 is switched off and the inductive motorwinding, motor or induction machine 55 induces the energy spike.Similarly, the fourth protection diode 115 may conduct to dissipatetransient energy associated with an electrical energy spike when thefourth switch 114 is switched off and the inductive motor winding ormotor induces the energy spike. An electric machine 55 or generator hasone or more windings (57, 157, 257). A second phase output terminal 153is associated with the switched terminals (154, 156) between the thirdswitch 112 and the fourth switch 114. In one configuration, the firstphase output terminal 53 is coupled to the first winding 53 and thesecond phase output terminal 153 is coupled to a second winding 157 ofthe induction machine 55 or generator. In some configurations, thefirst, second and third windings may be configured with a common node 56that is electrically grounded to ground, chassis ground, or chassisneutral.

A second phase driver 118 comprises a third power supply 122 and afourth power supply 124 that are controlled by, modulated by, orswitched by a driver module 614, controller or the electronic dataprocessing system 100. In one embodiment, the third power supply 122comprises a first voltage source 38 and a second voltage source 40.Meanwhile the fourth power supply 124 comprises a first voltage source38 and a second voltage source 40. In one embodiment, the second phasedriver 118 comprises a third biasing network 133; the third biasingnetwork 133 comprises a third set of blocking diodes 132 that arecascaded in series between one of the direct current terminals 28 and anode 137 associated with the third power supply 122 and a fifth controlswitch 142 (S₅) of the second phase driver 118. In one embodiment, thesecond phase driver 118 comprises a fourth biasing network 135; thefourth biasing network 135 comprises a fourth set of blocking diodes 134that are cascaded in series between the second phase output terminal 153and a node 139 associated with the fourth power supply 124 and a seventhcontrol switch 146 (S₇) of the second phase driver 118.

In one configuration, the first phase output terminal 53 and the secondphase output terminal 153 of the inverter 111 are connected in parallelto the induction machine 55 or to the respective phase windings of theinduction machine 55 to enhance collectively the output power capacityof the first power supply 22, the second voltage supply 24, the thirdvoltage supply 122 and the fourth voltage supply 124 to aid (e.g.,decrease the duration of the transitional excitation mode or increasethe slope of the ramp-up of the direct current voltage during thetransitional excitation mode from a start-up voltage to a target directcurrent operational voltage) in the self-excitation of an inductionmachine.

In one embodiment, the first output level provides electrical energy viathe first set of blocking diodes 32 and via the second set of blockingdiodes 34 to the capacitor 26 to charge or trickle charge the capacitor26 to achieve the start-up voltage level to start the self-excitation ofalternating current flux in one or more windings (of the inductionmachine 55) associated with the first phase output terminal 53 (e.g.,during the transitional excitation mode). In another embodiment, thefirst output level provides electrical energy via the third set ofblocking diodes 132 and via the fourth set of blocking 134 to thecapacitor to charge or trickle charge the capacitor 26 to achieve theprimary voltage level or start-up voltage level to start theself-excitation of alternating current flux in one or more windings (ofthe induction machine 55) associated with the second phase outputterminal 153 (e.g., during the transitional excitation mode).

One or more resistors may be associated with the third control terminal150 and the fourth control terminal 152. For example, a first inputresistor 20 (e.g., first gate resistor) is coupled between the thirdcontrol terminal 150 and a terminal of the fifth control switch 142(S₅), whereas a second input resistor 21 (e.g., second gate resistor) iscoupled between the third control terminal 150 and a terminal of thesixth control switch 144 (S₆). For example, a first input resistor 20(e.g., first gate resistor) is coupled between the fourth controlterminal 152 and a terminal of the seventh control switch 146 (S₇),whereas a second input resistor 21 (e.g., second gate resistor) iscoupled between the fourth control terminal 152 and a terminal of theeighth control switch 148 (S₈).

A third power supply 122 provides a first output voltage level and asecond output level switchable (via the fifth control switch 142 and thesixth control switch 144) to the third control terminal 150 of the thirdswitch 112, where the first output level is distinct from the secondoutput level. A fourth power supply 124 provides the first outputvoltage level and the second output level switchable (via the seventhcontrol switch 146 and the eighth control switch 148) to the fourthcontrol terminal 152 of the fourth switch 114.

In one embodiment, the third power supply 122 is associated with a node137 at the first output voltage level, where the fifth control switch(S₅) 142 controls or switches the electrical connection between the node137 and third control terminal 150 of the third switch 112; the thirdpower supply 122 is associated with a node at the second output voltagelevel, where the sixth control switch (S₆) 144 controls or switches theelectrical connection between the node at the second output level andthe third control terminal 150.

In one embodiment, a third power supply 122 (e.g., third voltage supply)provides a first output voltage level and a second output levelswitchable to the third control terminal 150 of the third switch 112.The first output level provides electrical energy via the third set ofblocking diodes 132 to the capacitor 26 to trickle charge the capacitor26 for self-excitation of alternating current flux in a second winding157 associated with the second phase output terminal 153.

Similarly, the fourth power supply 124 is associated with a seventhcontrol switch (S₇) 146 with switch terminals connected between thefourth control terminal 152 and a node 139 at the first output voltagelevel; the fourth power supply 124 is associated with an eighth controlswitch (S₈) 148 with switch terminals between a node at the secondoutput level and the fourth control terminal 152. A fourth voltagesupply 124 provides the first output voltage level and the second outputlevel switchable (via the seventh control switch 146 and the eighthcontrol switch 148) to the fourth control terminal 152 of the fourthswitch 114. The first output level provides electrical energy via thefourth set of blocking diodes 134 to the capacitor 26 to charge (e.g.,trickle) charge the capacitor 26 for excitation or self-excitation ofalternating current flux in the second windings 157 associated with thesecond phase output terminal 153.

In one configuration, the fifth control switch (S₅) 142 and the seventhcontrol switch (S₇) 146 are off, or inactive, during the start-up mode.During the start-up mode and prior to the operational mode (e.g.,generating mode of the induction machine 55), the third switch (B₁) 112and the fourth switch 114 B₂ are turned off. Further, in one embodiment,the sixth control switch 144 is on during the start-up mode to keep thethird switch (B₁) 112 off and the eighth control switch 148 is on duringthe start-up mode to keep the fourth switch (B₂) 114 off during thestart-up mode.

In the start-up mode, the third power supply 122 and the fourth powersupply 124 simultaneously each provide electrical energy at the firstvoltage level in series via the third set of blocking diodes 132 and thefourth set of blocking diodes 134 to the capacitor 26 to charge (e.g.trickle charge) the capacitor 26 for excitation or self-excitation ofelectromagnetic fields to produce (rotating and) alternating current inthe second winding 157 associated with the second phase output terminal153. Collectively, the voltage applied to charge (e.g., trickle charge)the capacitor 26 is approximately twice the first voltage level, lessvoltage drops in the forward biased diodes of the third set of diodes132 and the fourth set of diodes 134 and less the voltage drop in anyapplicable resistors 36.

In an operational mode after charging (e.g., fully charging or tricklecharging) the capacitor 26 to a startup-voltage or primary voltage(e.g., pre-charge voltage that is sufficient to enable the inverter orthe transitional mode), the first output level can be applied to theactivate the third switch 112 or the fourth switch 114, whereas thesecond output level is applied to deactivate the third switch 112 or thefourth switch 114 in accordance with a modulation commands (e.g., pulsewidth modulation commands) of the second phase driver 118, the drivercontroller or the electronic data processing system 100. As previouslyindicated, the start-up mode (e.g., weak pre-charge mode) and theoperational mode are mutually exclusive and do not occur simultaneously.

During an operational mode (e.g., or during the transitional excitationmode), the fifth control switch 142, the sixth control switch 144, theseventh control switch 146 and the eighth control switch 148 alternatebetween off and on in accordance with modulation commands (e.g.,pulse-width modulation (PWM)) from a controller or space vector pulsewidth modulation (SVPWM)) after self-excitation of the alternatingcurrent flux in one or more windings associated with the second phaseoutput terminal 153. Before the self-excitation scheme has beeninitialized, the third set of diodes 132 and the fourth set of diodes134 (and, more generally, diodes D₁ to D₆) are forward biased and chargethe capacitor 26 across the direct current voltage terminals (28, 30) toa start-up voltage or primary voltage, such as approximately 20 VDC oranother suitable charging voltage for charging (e.g., trickle-chargingor gradual charging) of the capacitor 26. During the transitionalexcitation mode or the operational mode, the third set of diodes 132 andthe fourth set of diodes 134 become reverse biased as the voltagebetween the direct current terminals (28, 30) rises above the start-upvoltage to an initial secondary voltage (e.g., 30 VDC).

During the transitional excitation mode (e.g., after the self-excitationscheme is initialized) or during the operational mode, the inductionmachine 55, the first set of diodes 32 and the second set of diodes 34become reverse biased as the voltage between the direct currentterminals (28, 30) rises or ramps up to a final, peak or steady-statesecondary voltage (e.g. high voltage of approximately 200 volts directcurrent or greater). For example, the final, peak or steady-statesecondary voltage may comprise the target operational direct currentvoltage at the end of the third time period, T3, or during the fourthtime period, T4, in FIG. 6B. In one embodiment, the secondary voltageequals the start-up voltage plus a transitional voltage that ramps up orthat changes over time before reaching the final, peak, steady-statesecondary voltage, or the target operational direct current voltage. Forexample, the secondary voltage may ramp up from approximately 30 voltsdirect current (VDC) to approximately 200 volts direct current orgreater, where the primary voltage as approximately 20 volts directcurrent.

Once the self-excitation scheme is initialized during the operationalmode, the second phase driver 118, the driver controller or electronicdata processing system 100 controls the switching states (on or offstates) of the third switch 112 and the fourth switch 114 in accordancewith a control scheme (e.g., pulse width modulation or space-vectorpulse width modulation). Accordingly, during the operational mode, thefifth control switch 142 and the sixth control switch 144 alternatebetween on and off, and the seventh control switch 146 and the eighthcontrol switch 148 alternate between on and off.

In one embodiment, the first output voltage level (e.g., +15 VDC) isgreater than the second output voltage level (e.g., −8 VDC), and thecapacitor 26 is charged to approximately twice the first voltage level,less a first voltage drop associated with the third set of diodes 132and a first resistor 36 in series with the third set of diodes 132 andless a second voltage drop associated with the fourth set of diodes 134and a second resistor 36 in series with the fourth set of diodes 134.Although the first resistor 36 and the second resistor 36 may comprise aone kilo-ohm resistor, any other suitable resistance may be used to set,limit or manage the level of the current that trickle charges thecapacitor 26.

In FIG. 2, the third phase of FIG. 2 comprises a fifth switch 212 havingfifth switched terminals 254 and a fifth control terminal 250. A sixthswitch 214 has sixth switched terminals 256 and a sixth control terminal252. The switched terminals (254, 256) of the fifth switch 212 and thesixth switch 214 are coupled in series between the direct currentvoltage terminals (28, 30).

In one embodiment, if the fifth switch 212 comprises a transistor, suchas a bipolar junction transistor on an IGBT, the fifth switchedterminals 254 comprise an emitter and a collector. The fifth controlterminal 250 of the fifth switch 212 may comprise a gate or a base ofthe fifth switch 212. In one embodiment, if the fifth switch 212comprises a field-effect transistor, the fifth switched terminals 256comprise a source and a drain. The fifth control terminal 250 of thefifth switch 212 may comprise a gate or a base.

Similarly, in one embodiment, if the sixth switch 214 comprises atransistor, such as a bipolar junction transistor or an IGBT, the sixthswitched terminals 256 comprise an emitter and a collector. The sixthcontrol terminal 252 of the sixth switch 214 may comprise a gate or abase of the sixth switch 214. In one embodiment, if the sixth switch 214comprises a field-effect transistor, the sixth switched terminals 256comprise a source and a drain. The sixth control terminal 252 of thesixth switch 214 may comprise a gate or a base of the sixth switch 214.

In the third phase, a protection diode or free-wheeling diode (213, 215)may be connected between the switched terminals of each switch toprotect the switch from transient currents that occur during switchingtransitions of the fifth switch 212 and the sixth switch 214. Forexample, a fifth protection diode 213 may conduct when the sixth switch214 is in an on state, whereas the sixth protection diode 215 mayconduct when the fifth switch 212 is in an on state.

An electric machine 55 or generator has one or more windings (57, 157,257). A third phase output terminal 253 is associated with the switchedterminals (254, 256) between the fifth switch 212 and the sixth switch214. In one configuration, the third phase output terminal 253 iscoupled to the third winding 257 of the induction machine 55 orgenerator. In some configurations, the first, second and third windingsmay be configured with a common node 56 that is electrically grounded toground, chassis ground, or chassis neutral.

A third phase driver 218 comprises a fifth power supply 222 and a sixthpower supply 224 that are controlled by, modulated by, or switched by adriver module 614, a driver controller or the electronic data processingsystem 100. In one embodiment, the fifth power supply 222 comprises afirst voltage source 38 and a second voltage source 40. Meanwhile thesixth power supply 224 comprises a first voltage source 38 and a secondvoltage source 40.

In one embodiment, the third phase driver 218 comprises a fifth biasingnetwork 233; the fifth biasing network 233 comprises a fifth set ofblocking diodes 232 that are cascaded in series between one of thedirect current terminals 28 and a node 237 associated with the fifthpower supply 222 and a terminal of a ninth control switch 242 (S₉) ofthe third phase driver 218. In one embodiment, the third phase driver218 comprises a sixth biasing network 235; the sixth biasing network 235comprises a sixth set of blocking diodes 232 that are cascaded in seriesbetween the third phase output terminal 253 and a node 239 associatedwith the sixth power supply 224 and an eleventh control switch 246 (S₁₁)of the third phase driver 218.

One or more resistors may be associated with the fifth control terminal250 and the sixth control terminal 152. For example, a first inputresistor 20 is coupled between the fifth control terminal 250 and aterminal of the ninth control switch 242, whereas a second inputresistor 21 is coupled between the fifth control terminal 250 and aterminal of the tenth control switch 244. For example, a first inputresistor 20 is coupled between the sixth control terminal 252 and aterminal of the eleventh control switch 246, whereas a second inputresistor 21 is coupled between the sixth control terminal 252 and aterminal of the twelfth control switch 248.

A fifth power supply 222 provides a first output voltage level and asecond output level switchable (via the ninth control switch 242 or thetenth control switch 244) to the fifth control terminal 250 of the fifthswitch 212, where the first output level is distinct from the secondoutput level. A sixth power supply 224 provides the first output voltagelevel and the second output level switchable (via the eleventh controlswitch 246 or the twelfth control switch 248) to the sixth controlterminal 252 of the sixth switch 214.

In one embodiment, the fifth power supply 222 is associated with a node237 at the first output voltage level, where the ninth control switch(S₉) 242 controls or switches the electrical connection between the node237 and fifth control terminal 250 of the fifth switch 212 (C₁); thefifth power supply 222 is associated with a node at the second outputvoltage level, where the tenth control switch (S₁₀) 244 controls orswitches the electrical connection between the node at the second outputlevel and the fifth control terminal 250. In one embodiment, a fifthpower supply 222 (e.g., fifth voltage supply) provides a first outputvoltage level and a second output level switchable to the fifth controlterminal 250 of the fifth switch 212. The first output level provideselectrical energy via the fifth set of blocking diodes 232 to thecapacitor 26 to charge (e.g., trickle charge) the capacitor 26 forexcitation or self-excitation of alternating current flux in the thirdwinding 257 associated with the third phase output terminal 253.

Similarly, the sixth power supply 224 is associated with an eleventhcontrol switch (S₁₁) 246 with switch terminals connected between thesixth control terminal 252 and a node 239 at the first output voltagelevel; the sixth power supply 224 is associated with a twelfth controlswitch (S₁₂) 248 with switch terminals between a node at the secondoutput level and the sixth control terminal 252. A sixth power supply224 provides the first output voltage level and the second output levelswitchable to the sixth control terminal 252 of the sixth switch 214(C₂). The first output level provides electrical energy via the sixthset of blocking diodes 234 to the capacitor 26 to charge (e.g., tricklecharge) the capacitor 26 for excitation or self-excitation ofalternating current flux in the third winding 257 associated with thethird phase output terminal 253.

In one configuration, the ninth control switch (S₉) 242 and the eleventhcontrol switch (S₁₁) 246 are off, or inactive, during the start-up mode(e.g., weak pre-charge mode). During the start-up mode and prior to theoperational mode (e.g., generating mode of the induction machine 55),the fifth switch (C₁) 212 and the sixth switch (C₂) 214 are turned off.Further, in one embodiment, the tenth control switch 244 is on duringthe start-up mode to keep the fifth switch (C₁) 212 off and the twelfthcontrol switch 248 is on during the start-up mode to keep the sixthswitch (C₂) 214 off during the start-up mode.

In a start-up mode (e.g., weak pre-charge mode), the fifth power supply222 and the sixth power supply 224 simultaneously each provideelectrical energy at the first voltage level in series via the fifth setof blocking diodes 232 and the sixth set of blocking diodes 234 to thecapacitor 26 to charge (e.g., trickle charge) the capacitor 26 forexcitation or self-excitation electromagnetic fields to produce(rotating and) alternating current in the third windings 257 associatedwith the third phase output terminal 253 (e.g., to enable entry into thetransitional excitation mode). Collectively, the voltage applied tocharge (e.g., trickle charge) the capacitor 26 is approximately twicethe first voltage level, less voltage drops in the forward biased diodesof the fifth set of diodes 232 and the sixth set of diodes 234 and lessthe voltage drop in any applicable resistors 36.

In an operational mode after charging (e.g., partially or fullycharging) the capacitor 26 to a start-up voltage or primary voltage(e.g., sufficient to enable activation of the inverter switches), thefirst output level can be applied to the activate the fifth switch 212or the sixth switch 214, whereas the second output level is applied todeactivate the fifth switch 212 or the sixth switch 214 in accordancewith a modulation commands (e.g., pulse width modulation commands) ofthe third phase driver 218, the driver controller or the electronic dataprocessing system 100. The start-up mode (e.g., weak pre-charge mode)and the operational mode are mutually exclusive and do not occursimultaneously.

During an operational mode (e.g., or in the transitional excitationmode), the ninth control switch 242, the tenth control switch 244, theeleventh control switch 246 and the twelfth control switch 248 alternatebetween off and on during an operational mode in accordance withmodulation commands (e.g., pulse-width modulation (PWM)) from acontroller or space vector pulse width modulation (SVPWM)) afterself-excitation of the of alternating current flux in one or morewindings associated with the third phase output terminal 253. Before theself-excitation scheme has been initialized, the fifth set of diodes 232and the sixth set of diodes 234 (and, more generally, diodes D₁ to D₆)are forward biased and charge the capacitor 26 across the direct currentvoltage terminals (28, 30) to a start-up voltage or primary voltage,such as approximately 20 VDC or another suitable charging voltage forcharging (e.g., trickle-charging or gradual charging) of the capacitor26. During the transitional excitation mode or during the operationalmode, the fifth set of diodes 232 and the sixth set of diodes 234 becomereverse biased as the voltage between the direct current terminals (28,30) rises above the start-up voltage to an initial secondary voltage(e.g., 30 VDC) from induced energy of the electromagnetic fields in theinduction machine.

During the transitional excitation mode (e.g., after the self-excitationscheme is initialized) or during the operational mode of the inductionmachine 55, the fifth set of diodes 232 and the sixth set of diodes 234become reverse biased as the voltage between the direct currentterminals (28, 30) rises or ramps up to a final, peak or steady-statesecondary voltage (e.g. high voltage of approximately 200 volts directcurrent or greater) from induced energy of the electromagnetic fields inthe induction machine subject to rotational energy applied to its rotor.

In one embodiment, the secondary voltage equals the start-up voltageplus a transitional voltage that ramps up or changes over time during atransitional excitation mode before reaching the final, peak,steady-state secondary voltage, or target operational direct currentvoltage. For example, the secondary voltage may ramp up fromapproximately 30 volts direct current (VDC) to approximately 200 voltsdirect current or greater, where the primary voltage as approximately 20volts direct current.

Once self-excitation scheme is initialized or during the operationalmode, the third phase driver 218, the driver controller or electronicdata processing system 100 controls the switching states (on or offstates) of the fifth switch 212 and the sixth switch 214 in accordancewith a control scheme (e.g., pulse width modulation or space-vectorpulse width modulation). Accordingly, during the operational mode, theninth control switch 242 and the tenth control switch 244 alternatebetween on and off, and the eleventh control switch 246 and the twelfthcontrol switch 248 alternate between on and off.

In one embodiment without limiting the scope of the disclosure orappended claims, the first output voltage level (e.g., +15 VDC) isgreater than the second output voltage level (e.g., −8 VDC), and thecapacitor 26 is charged to approximately twice the first output voltagelevel, less a first voltage drop associated with the fifth set of diodes232 and a first resistor 36 in series with the fifth set of diodes 232and less a second voltage drop associated with the sixth set of diodes234 and a second resistor 36 in series with the sixth set of diodes 234.Although the first resistor 36 and the second resistor 36 may comprise aone kilo-ohm resistor, any other suitable resistance may be used to set,limit or manage the level of the current that trickle charges thecapacitor 26.

In summary, before the self-excitation scheme is initialized totransition to or facilitate the operational mode and during the start-upmode (e.g., weak pre-charge mode), the switches A₁, A₂, B₁, B₂, C₁, C₂are turned off. Once self-excitation scheme is initialized during thetransitional excitation mode and during the operational mode, theswitches A₁, A₂, B₁, B₂, C₁, C₂ are gated or controlled by theelectronic data processing system 100 as per the control scheme inaccordance with the software instructions or modules described inconjunction with FIG. 5A, or otherwise. However, during the transitionalexcitation mode a load (on the direct current bus, such as an invertercoupled to a motor 302, a battery 304, a resistive load 306) may bereduced, limited, reactance-managed, impedance-restricted, ordisconnected from the direct current bus or the output of the inductionmachine 55 to support the ramping up of the direct current voltage tothe full operational target direct current voltage.

The generator comprises an induction machine 55 (e.g., a squirrel cageinduction machine 55) without any energy storage device connectedbetween the direct current voltage terminals (28, 30), except for thecapacitor 26, and without any capacitor 26 connected to the first phaseoutput terminal 53 (or any other alternating current terminal of theinduction machine 55). In one configuration, the induction machine 55does not include any permanent magnets in or for the rotor.

In certain configurations, the generator generates an operationalvoltage level exceeding approximately six hundred (600) volts, such asapproximately seven hundred (700) volts, during an operational modeafter the capacitor 26 is trickle-charged during the start-up mode to astart-up voltage level that exceeds approximately fifteen (15) volts,such as approximately twenty (20) volts to approximately thirty (30)volts.

FIG. 3A is another embodiment of a schematic representation of aninverter system 111 that is connected to an induction generator 55, anactive load 300 that comprises a secondary inverter 211 and an electricmotor 302, and a passive load that comprises a resistive load 306 or adisconnectable resistive load. In practice, the active load 300 isdisabled or disconnected by the controller or data processing system 100during excitation of the inverter system 111 or primary inverter. Likereference numbers in FIG. 2 and FIG. 3A indicate like elements.

In one embodiment, a secondary inverter 211 comprises a pair of inputcontrol terminals (380, 381, 382) for each phase (397, 398, 399) and anoutput terminal (353, 453, 553) for each phase. Each phase (397, 398,399) comprises an upper switch (312, 412, 512) and a lower switch (314,414, 514) with switched terminals (371, 372, 373, 374, 375, 376) thatare coupled together at the output terminal (353, 453, 553) from eachphase. Other switched terminals (371, 372, 373, 374, 375, 376) of theupper switch (312, 412, 512) and the lower switch (314, 414, 514) arecoupled to the direct current voltage terminals (28, 30) (e.g., directcurrent bus). The input control terminals (380, 381, 382) are connectedto or associated with a driver module 614 or electronic data processingsystem 100 for controlling the states of the upper switch (312, 412,512) and the lower switch (314, 414, 514) for each phase in accordancewith a controller 106 or electronic data processing system 100. Asillustrated, the secondary inverter has three phases with phase outputterminals 353 (A*), phase 453 (B*) and phase 553 (C*).

In one embodiment, the induction machine 55 of FIG. 3A comprises aninduction generator with a shaft that is rotated or driven by a primemover, an internal combustion engine, or another source of rotationalenergy. The windings of the induction machine 55 are self-excited by thecapacitor 26 to support generation or conversion of the rotationalenergy of the induction machine 55 into electrical energy.

The output phase terminals (53, 153, 253) of the inverter system 111 orprimary inverter are coupled to one or more windings of the inductiongenerator 55 (e.g., self-excited squirrel-cage induction machine) andreceive alternating current generated by the induction generator 55. Theinverter system 111 or primary inverter convers the alternating currentreceived from the induction generator into direct current to charge thecapacitor 26 across the direct current voltage terminals (28, 30) (e.g.DC bus) and to provide electrical energy to one or more active loads 300or passive loads (e.g., 306).

In one configuration, the secondary inverter 211 and the electric motor302 comprise an active load 300 on the generator. The secondary inverter211 uses the electrical energy on the direct current voltage terminals(28, 30) to provide or output alternating current at the outputterminals (353, 453, 553), such as phase A*, phase B* and phase C*,which are coupled to the motor 302. A data processing system 100 orcontroller controls the inputs of the secondary inverter 211 inaccordance with a modulation scheme, such as pulse width modulationscheme at the control terminals of the switches to product a suitablealternating current signal (e.g., one or more substantially sinusoidalsignals or other suitable waveforms) for controlling the torque,velocity, speed and direction of the motor 302. An electric motor 302 iscoupled to the alternating current output terminals. The secondaryinverter 211 is adapted to control the electric motor 302 throughsignals provided at the alternating current output terminals.

During excitation through one or more switches in series with directcurrent voltage terminals (28, 30, or both), the controller or dataprocessing system 100 can disable or disconnect the active load 300 fromthe primary inverter or inverter system 111.

A resistive load 306 or a load may be placed across the terminals of thedirect current voltage terminals (28, 30) if or when the inverter system111 or primary inverter is operating in the operational mode after thestart-up mode. The disconnect switch 303 is used to connect ordisconnect the resistive load 306, inductive load, or other load to thedirect current voltage terminals (28, 30) at an appropriate time, suchas during the operational mode or to transition the disconnect switch303 to an on state upon completion of the start-up mode.

FIG. 3B is another embodiment of a schematic representation of aninverter system 111 that is connected to an induction generator 55, anactive load 300 that comprises a secondary inverter 211 and an electricmotor 302, and a battery 304. The system of FIG. 3B is similar to thesystem of FIG. 3A except the resistive load 306 of FIG. 3A is replacedby the battery 304 of FIG. 3B. Like reference numbers in FIG. 3Bindicate like elements or features in FIG. 2 and FIG. 3A.

In the embodiment of FIG. 1, FIG. 2, and FIG. 3A, there is no battery304 between the direct current voltage terminals (28, 30) (e.g., directcurrent bus terminals) and only the capacitor 26 (e.g., electrolyticcapacitor 26) is used to excite the windings of the induction machine 55or induction generator. However, in an alternate embodiment of FIG. 3B abattery 304 is coupled between the direct current voltage terminals (28,30), and may have a direct current voltage interface to step-up orstep-down the voltage to the proper level for maintenance, charging anddischarging of the battery 304. As indicated previously, the chargedcapacitor 26 alone (without any battery 304) can excite the windings inthe induction machine 55 or induction generator. Further, in thealternate embodiment, the charged capacitor 26 can alone (e.g., chargedto a primary voltage around 20 volts direct current) excite the windingsin the induction generator 55, alone or together with the battery 304,can excite the windings in the induction generator 55.

In another alternate embodiment, the electrical direct current load orbattery 304 is coupled to the direct current terminals (28, 30) via aload disconnect switch 303 that is off (or in an open state) during astart-upstage (e.g., during the start-up mode and during self-excitationin the transitional excitation mode) and on (or in a closed state orconducting state) during an operational mode. In practice, during thestart-up stage or excitation stage the battery 304 can be disconnectedand not used for excitation and the controller 106 can disable or canelectrically isolate the inverter from any active induction machine 55or motor during excitation. For instance, a data processor 128 orelectronic data processing system 100 controls a disconnect switch 303:(1) to decouple (e.g., optionally) the electrical direct current load orbattery 304 between the direct current terminals during a start-up modeor during a start-up stage, and/or (2) to couple the electrical directcurrent load or battery 304 between the direct current terminals duringthe operational mode (e.g., during power generation of the inductiongenerator 55 or machine) and after (not during) the start-up mode orstart-up stage (e.g., during charging of the capacitor 26).

Here, a discharged battery, which can amount to battery 304 from time totime, can be modeled as a resistive load or reluctance load. In otherwords, the load or battery is connected to the direct current terminals(28, 30) after self-excitation or the self-excitation stage of thewindings in the induction machine 55 are complete such that the load(304 or 306) can use the electrical energy generated by the inductionmachine 55 or induction generator. In certain configurations, thestart-up mode and transitional excitation mode do not require a chargedbattery (e.g. but can optionally use a charged battery to increase theramp up or rise rate versus time in the direct current voltage busduring the transitional excitation mode) to excite the induction machine55 in preparation for the operational mode. In practice, the electronicdata processing system 100 or driver controller may issue an excitationcomplete signal or status message to switch from the start-up mode tothe operational mode.

FIG. 4 is yet another embodiment of a schematic representation of aninverter system 111 that is connected to an induction generator 55, anactive load 300 that comprises a secondary inverter 211 and an electricmotor 302. The system of FIG. 4 is similar to the system of FIG. 3A,except the system of FIG. 4 has no resistive load and no disconnectswitch associated with the load. Like reference numbers in FIG. 2, FIG.3A, and FIG. 4 indicate like elements or features. The description ofFIG. 3A and FIG. 3B apply to FIG. 4, except for the references to theresistive load 306, the battery 304, and the disconnect switch 303 as iffully set forth in conjunction with FIG. 4.

FIG. 5A is a block diagram that illustrates one possible embodiment ofthe modules associated with the electronic data processing system 100for controlling the driver module 614 and/or the drivers (18, 118, 218)for the inverter system 111, 211 or both. As used throughout thisdocument, a module or component may refer to software, hardware or both.The lines that interconnect the modules may represent physicaltransmission lines, or virtual communications or relationships betweenmodules. For example, physical transmission lines include wires, cables,coaxial cables, conductive traces on circuit boards, or otherconductors; whereas virtual communications may refer to communicationsof data, such as calls, between software or other data structures.Software shall mean software instructions, data files, databases,look-up tables, equations, curves, mathematical relationships, logicrelationships, and other data structures for storing data.

As used throughout this document, configured to, adapted to, andarranged to shall be considered synonymous and shall mean any of thefollowing: (a) programmed or equipped with software instructions, logicor data structures to accomplish a specified function, process,determination, or result, or (b) equipped with hardware, circuits orelectronics to accomplish a function, process, determination, or result,or (c) capable of performing a function, process or calculation whilethe system or inverter is working or operational.

In one embodiment, the electronic data processing system 100 comprisesan electronic data processor 128, a data storage device 120 and one ormore data ports 101 coupled to a data bus 126. The data storage device120 may store, retrieve, read and write data with respect to one or moremodules or components illustrated in FIG. 5A. FIG. 5A is merely onepossible illustrative representation of the software modules, look-uptables, and data processing system 100 that can be used to implement anembodiment of the system and method disclosed in this document, andother configurations or data processing systems are possible.

The electronic data processor 128 may comprise a processor, amicrocontroller, a digital signal processor, an application specificintegrated circuit (ASIC), a programmable logic array, a programmablelogic device, field programmable gate array (FPGA), a logic circuit, anarithmetic logic unit, a Boolean logic device, or another dataprocessing device. Any of the software modules, look-up tables or datastructures, mathematical operations, transformations, controllers, orother blocks referenced in FIG. 5A or elsewhere this disclosure may berealized by the data processor 128, alone or in combination with thedata storage device 120. For example, the data processor 128 may processor manipulate data, algorithms and software instructions stored inregisters or accessed by the data processor 128 in the data storagedevice 120 to carry out the functions, controllers, calculators,selectors, or modules described in this document.

Each data port 101 may comprise a data transceiver, buffer memory, orboth.

The data storage device 120 may comprise one or more of the following:electronic memory, nonvolatile electronic memory, an optical datastorage device, a magnetic data storage device, or other device forstoring digital or analog data.

In one embodiment, the driver controller comprises an electronic dataprocessing system 100 for controlling an inverter (11, 111 or 211), suchas an inverter coupled to an induction machine (e.g., 55) or inductiongenerator.

A voltage sensor 575 is configured to measure an observed voltage acrossthe direct current voltage terminals (28, 30) (e.g., DC bus). Forexample, the voltage sensor 575 provides an observed voltage to theelectronic data processing system 100 via a data port 101. A referencevoltage source 102 provides a reference DC bus voltage. For example, thereference voltage source 102 provides the reference DC bus voltage tothe electronic data processing system 100 via a data port 101. In oneembodiment, the reference voltage source 102 may comprise a comparator,an operational amplifier or a voltage regulator circuit (e.g., such as aramped reference signal versus time).

A voltage difference module 104 is configured to determine a voltagedifference (e.g., voltage bus error) between the observed voltage (ofthe voltage sensor 575) and a reference DC bus voltage. The voltagedifference module 104 outputs or provides the voltage difference betweenthe observed voltage and the reference DC bus voltage to a controller106.

A controller 106, such as a proportional integral (PI) controller 106,is adapted to generate a reference quadrature-axis (q-axis) currentcommand (I_(q) ^(ref)) based on the voltage difference between theobserved voltage and the reference DC bus voltage (e.g., at terminals28, 30) to a controller 106.

A current sensor 577 can measure one or more phase currents that relateto a q-axis current (I_(q) ^(measured)). In one embodiment, a currentsensor 577 is coupled to a data port 101; the current sensor 577facilitates the provision of a measured q-axis current to the electronicdata processing system 100. For example, one or more current sensors 577measure current for each phase of the induction machine 55, such asI_(a), I_(b), and I_(c), where the inputs of a Parks transformationmodule 615 is coupled to an output of each current sensor 577 such thatthe Parks transformation module 615 transforms the measured currentsinto a measured q-axis current, or into a measured q-axis current and ameasured d-axis current.

A current difference module 108 is adapted to determine a currentdifference (e.g., q-axis current error) between the measured q-axiscommand current and the reference q-axis current command (I_(q) ^(ref)).

A first current regulator 110 is configured to output a q-axis voltagecommand (V_(q)) (or its equivalent q-axis current command) based on aninput of the current difference between the measured q-axis commandcurrent and the reference q-axis current command (I_(q) ^(ref)). Thefirst current regulator 110 provides the q-axis voltage command (V_(q))(or its equivalent q-axis current command) to the Inverse Parkstransformation module 612 and the residual voltage calculator 116. Theinverse Parks transformation module 112 uses the q-axis voltage command(or its equivalent q-axis current command), the measured rotor positionand slip angle to provide appropriate control signals to the drivermodule 614. In one embodiment, the driver module 614 has outputterminals for controlling the inverter switches (e.g., 12, 112, 212, 14,114, 214). For example, the output terminals of the driver module 614are coupled to the phase drivers (18, 118, 218) or to the controlterminals (50, 150, 250, 52, 152, 252).

Residual voltage is the alternating current output at one or more phaseoutput terminals of the induction machine 55 that persists and decaysduring a transient time period after direct current voltage excitationof the direct current bus is turned off. However, during operation ofthe induction machine (e.g., application of rotational energy to themachine's rotor) the residual voltage and the associated electromagneticfields in the electric machine can contribute toward the excitation ofthe induction machine 55 in the transitional excitation mode. Residualdirect-axis voltage is a transformation (e.g., Parks transformation)that represents the alternating current residual current in simplifiedform for computation. In one embodiment, the data processor 128 isprogrammed with software instructions or otherwise adapted to inflatethe residual direct-axis current to increase the robustness of anexcitation process of the electromagnetic field in the one or morewindings and the associated increase in direct current voltage.

An electronic data processor 128 or residual voltage calculator 116determines a direct-axis (d-axis) residual voltage (V_(d) ^(residual))based on the q-axis voltage command and an observed voltage across thedirect current voltage terminals (28, 30) (e.g., DC bus). For example,the data processor 128 or residual voltage calculator 116 determines ad-axis residual voltage (V_(d) ^(residual)) in accordance with thefollowing equation (e.g., to fully use the DC bus and facilitate robust,reliable self-excitation of the windings of the induction machine):

${V_{d}^{residual} = \sqrt{\frac{\left( {mV}_{DC}^{measured} \right)^{2}}{3} - V_{q}^{2}}};$where

V_(d) ^(residual) is the residual direct-axis voltage;

m is the modulation index;

V_(DC) ^(measured) is the measured voltage of or between the directcurrent terminals; and

V_(q) is the quadrature-axis voltage command.

The data processor 128 is adapted to determine d-axis reference current(I_(d) ^(ref)) for a corresponding residual d-axis voltage (V_(d)^(residual)) based on a magnetizing curve or K-factor lookup table 118stored in a data storage device 120. The data associated with themagnetizing curve or K factor lookup table 118 will typically vary basedon the characteristics and design of the respective induction machine orparticular induction generator.

In an alternate embodiment, the magnetizing curve or K-factor lookuptable 118 may be represented as one or more quadratic equations,graphical curves, data files, inverted files, or otherwise.

A current difference module 122 is adapted to determining an electricalcurrent difference (e.g., d-axis current error) between the measuredd-axis command current (e.g., observed d-axis current) and the referenced-axis current command (I_(d) ^(ref)). The current difference module 122provides the current difference (e.g., d-axis current error) to a secondcurrent regulator 124.

The second current regulator 124 (e.g., complex vector currentregulator) is adapted to determine the commanded d-axis voltage (V_(d))based on the current difference (e.g., d-axis current error) or themeasured d-axis current (I_(d) ^(measured)) and the determined d-axisreference current (I_(d) ^(ref)).

In one embodiment, an inverse Parks transformation module 612 canprovide or provides phase voltage commands (V_(a), V_(b), V_(c)) basedon inverse parks transform of the commanded voltages (V_(d) and V_(q)).For example, the inverse Parks transformation module 612 can provide orprovides phase voltage commands (V_(a), V_(b), V_(c)) based on inverseparks transform of the commanded voltages (V_(d) and V_(q)) and theelectrical angular position of the rotor (θ_(e)) of the inductionmachine 55 or generator. In particular, the Parks transformation modulecan use the following equation of the rotor field orientation to providephase voltage commands (V_(a), V_(b), V_(c)):θ_(e)=θ_(rotor)+∫ω_(slip) dt,

where θ_(e) is the electrical angular position of the rotor;

where θ_(roto) is the mechanical angular position of the rotor;

and ω_(slip) is the angular slip velocity of the rotor.

In certain embodiments, the sensor, such as a resolver encoder, canestimate or measure mechanical angular position of the rotor. In otherembodiments, such as the configuration illustrated in FIG. 5A, asensor-less position estimator can be used to estimate the mechanicalangular position of the rotor from current measurements by one or morecurrent sensors 577 that measure current of one or more phases of thealternating current output of the induction machine 55. The inverseParks transformation module 612 can provide the output of one or morephase voltage commands to driver module 614 or one or more drivers (18,118, 218) associated with an inverter. Typically, the output of thevoltage commands are consistent with pulse-width modulation orspace-vector pulse width modulation of the switching transistors of theinverter (11, 111, 211).

FIG. 5B is a block diagram of one possible embodiment of a system 500for controlling a mode of operation of an inverter (11, 111, 211).

In one embodiment, the system 500 may be incorporated into the dataprocessing system 100 of FIG. 5A or the system 500 may comprisesoftware, instructions or data structures that reside in the dataprocessing system 100 of FIG. 5A. For example, the system 500 may berealized by or implemented by the data processor 128 operating inconjunction with the data bus 126, data storage device 120, and otherblocks in FIG. 5A.

In some embodiments, the output of final direct-axis current command(I_(d) ^(*Final)) in FIG. 5B can be used as the reference direct-axiscurrent (I_(d) ^(Ref)) in FIG. 5A; the output of the finalquadrature-axis current command (I_(q) ^(*Final)) in FIG. 5B can be usedas the reference quadrature-axis current (I_(q) ^(Ref)) in FIG. 5B. Thevoltage proportional integral controller 514 of FIG. 5B is analogous toor a variant of the controller 106 of FIG. 5A; the mag curve look-uptable 118 of FIG. 5A is analogous to or a variant of the magnetizingcurve 516 of FIG. 5B.

In FIG. 5B, one or more of the following modules can communicate witheach other: the inverter mode controller 502, the excitation module 504,the switching module 506, the detection module 534, and the operationalmode module 536. The lines that connect the blocks or modules in FIG. 5Aand FIG. 5B represent virtual communication lines, physicalcommunication lines, or both, where physical communication lines mayrepresent transmission lines, conductors, or cables, or wirelesscommunication channels, and where virtual communication lines may becommunications of data via data bus, calls or data messages in asoftware program.

The inverter mode controller 502 can operate or control an inverter (11,11, 211) in accordance with one or more of the following operationalmodes: voltage control mode, torque command control mode, speed controlmode, and direct control mode. Further, the inverter mode controller 502supports the start-up mode, the transitional excitation mode, and theoperational mode, and optionally the hand-off mode (e.g., hysteresismode). The hand-off mode is an optional transition mode between thetransitional excitation mode and the operational modes. For example, thehand-off mode can assure that excitation in the transitional excitationmode is complete prior to entry into the operational mode in which theinverter and induction machine can be permitted to receive a full loadthat might otherwise be disruptive to completion of the transitionalexcitation mode and attainment of the full operational direct currentbus voltage. In the hand-off mode, the data processor 128 or a timer maydetermine that the excitation is complete and has reached the targetoperational direct current voltage by a hysteresis algorithm or by atimer (or data processor) that is triggered when the target operationaldirect current voltage meets or exceeds a threshold voltage for at leasta minimum time period (e.g., defined by a duration of one or moresampling intervals).

For operation in the operational mode, the mode controller 502 disablesthe excitation module 504 (e.g., via the excitation enable signal) andthe detection module 534 and enables the operational mode module 536. Inone embodiment, the inverter mode controller 502 determines that statesof one or more switches (508, 510) in the switching module 506 to selectthe final quadrature-axis current command (I_(q) ^(*Final)) and thefinal direct-axis current command (I_(d) ^(*Final)) from inputs of theexcitation direct-axis current command (I_(d) ^(exe*)), the normaldirect-axis current command (I_(dnormal*)) the excitationquadrature-axis current command (I_(q) ^(exc*)) the normalquadrature-axis current command (I_(qnormal*)), and operational modedata.

During the excitation of the induction machine (55) in a start-up modeor in the transitional excitation mode, the data processing system (100,500) or the inverter mode controller 502 controls one or more switches(508, 510) to output an excitation direct-axis current command (I_(d)^(exc*)) and an excitation quadrature-axis current command (I_(d)^(*Final)) from the excitation module 504 as the final direct-axiscurrent command (I_(d) ^(*Final)) and the final quadrature-axis currentcommand (I_(q) ^(*Final)), respectively. Similarly, after the excitationand during the operational mode, the data processing system (100, 500)or inverter mode controller 502 controls one or more switches (508, 510)to output a normal direct-axis current command (I_(dnormal*)) and anormal quadrature-axis current command (I_(qnormal*)) as the finaldirect-axis current command (I_(d) ^(*Final)) and the finalquadrature-axis current command (I_(q) ^(*Final)), respectively, whichdepends upon selection of the operational mode (e.g., voltage, torque,speed or direct control modes).

During the excitation, the data processing system (100, 500) operates inaccordance with FIG. 5A, where a variant is summarized in the excitationmodule 504 of FIG. 5B. The excitation module 504 receives the inputs of:(a) the commanded voltage (Vcmd*), which is composed of direct-axisvoltage and quadrature-axis voltage; (b) direct current voltage(VDC_measured) of the direct current data bus, and (c) the direct-axisresidual voltage (VRes). The excitation module 504 outputs an excitationdirect-axis current command (I_(d) ^(exc*)) and an excitationquadrature-axis current command (I_(q) ^(exc*)) based on DC bus voltagebuild-up module 512, a voltage proportional integral controller 514 anda magnetizing curve 516. In particular, the DC bus voltage buildupmodule 512 controls the an excitation direct-axis current command (I_(d)^(exc*)) and an excitation quadrature-axis current command (I_(q)^(exc*)) during the start-up mode and the transitional excitation modeto increase or ramp up the direct current voltage on the capacitor 26 oracross the direct current bus of the inverter. Further, the magnetizingcurve 516 is used to derive the direct-axis reference current, which canbe modified by the saturation module 520 (e.g., by a rate factor,I_(drated)) to enhance the increase or ramp-up of the voltage of thedirect current bus of the inverter in accordance with one or more targetslopes or slew rates (e.g., that are matched or optimized for windinginductances, target rotor speed range and other parameters of acorresponding induction machine 55).

After the excitation and during the operational mode, the dataprocessing system (100, 500) or the detection module 534 recognizes thatthe excitation is complete by evaluating the direct current bus voltagewith respect to the target direct current voltage, or the stop setvoltage plus a tolerance, as described in this document. In accordancewith one embodiment of a hysteresis algorithm, the detection module 534comprises a hand-off module 524 (e.g., hysteresis module) to determinewhether the measured direct current bus voltage is equal to or greaterthan a voltage threshold (e.g., stop set voltage plus a tolerance forone or more sampling periods) indicative of complete excitation of thewindings of the induction machine (55). If the detection module 534 orthe hand-off module 524 determines that the excitation is completebecause the voltage threshold is satisfied for a minimum time period,the hand-off module 524 generates an excitation complete signal or datamessage, which may be inputted to one or more Boolean logic blocks (526,528), such as the NOT device 526 and the OR device 528.

If the excitation is complete, the data processing system (100, 500) orinverter control module 502 activates the operational mode module 536and enters into the operational mode where the normal direct-axiscurrent command (I_(dnormal*)) and a normal quadrature-axis currentcommand (I_(dnormal*)) are outputted by a torque command module 532. Forexample, the normal voltage proportional integral controller 530 can usea commanded voltage (Vcmd*) or torque command, a measured direct currentvoltage (VDC_measured), and an enable or reset input (Reset) to controlthe selection of or the operational mode (e.g., to develop normaldirect-axis and quadrature-axis currents based on a torque command).During the operational mode, the excitation module 504 is disabled orthe excitation direct-axis current command (I_(d) ^(exc*)) and anexcitation quadrature-axis current command (I_(q) ^(exc*)) are set equalto zero as reflected in block 518. For example, the normal voltageproportional integral controller 530 may be implemented in accordancewith FIG. 5A in which the controller 106 and current regulator 124 cancarry out the functions of controller 530.

In one embodiment, the torque command module 532 determines direct-axisand quadrature-axis currents based on torque command generated by a useror software of the induction machine and whether the rotor of theinduction machine is operating at or below a baseline speed or velocity,such that the normal direct-axis current command and a normalquadrature-axis current command are outputted to target the baselinespeed or velocity with minimal error.

FIG. 6A is a chart that represents one embodiment of the ramping orincreasing of the direct current excitation voltage in the capacitor 26versus time, or across the DC bus terminals (28, 30), during thestart-up mode or during the start-up mode and during the transitionbetween the start-up and the operational mode, among other things. Forinstance, the chart of FIG. 6A may represent actual experimental resultsof an inverter that is self-excited to operate an induction machine 55.The horizontal axis 602 of FIG. 6A represents time, the vertical axis(601, 600) represents signal magnitude (in accordance with thecorresponding scales on the right or left of the chart). As shown, theleft vertical scale 601 represents volts direct current on the directcurrent bus of the inverter (e.g., inverter system 111), whereas theright vertical scale 600 represents direct-axis current divided byquadrature-axis current, which can be expressed as a unitless ratio.

As illustrated in FIG. 6A, the DC bus voltage 606 on the direct currentvoltage terminals (28, 30) ramps up from the start-up voltage to a peakoperational voltage or target direct current operational voltage, suchas 600 Volts or greater on the direct current bus or the direct currentvoltage terminals (28, 30). In the transitional excitation mode of FIG.6A (e.g., between approximately 0.1 seconds and 1 second of thehorizontal axis 602), the direct current ramps up to a targetoperational direct current voltage at a generally fixed slope or isslewed appropriate to ensure correct operation, although multiple rampup rates, slopes, or slew rates are possible. Although FIG. 6Aillustrates a peak operational voltage 607 of approximately 700 volts(direct current), the actual voltage depends upon design choices andfactors and the 700 volts level is merely one possible illustrativeexample.

FIG. 6A also illustrates: (1) the corresponding commanded direct-axiscurrent curve 605, labeled I_(d) ^(command), and indicated byalternating long and short dashed lines; (2) the correspondingquadrature-axis current curve 603, labeled Iq^(command), and indicatedby dashed lines; (3) the DC bus voltage 606, indicated by a solid line,and (4) the slewed direct current bus command 604, indicated by the longdashed lines, which is generally coextensive with the DC bus voltage606, as illustrated, and is associated with the operation of theinduction generator in combination with the inverter.

FIG. 6B is an illustrative chart that represents another possiblewaveform in the ramping up of the excitation voltage in the capacitorversus time during the start-up mode, transitional excitation mode andthe operational mode, among other things. In FIG. 6B, the horizontalaxis 650 represents time (e.g., in seconds) and the vertical axis 652represents actual direct current voltage (V_(DC) ^(actual)) on thedirect current bus.

A start-up mode is associated with a first time period, T₁, 654; atransitional excitation mode is associated with a second time period,T₂, 656; and an optional hand-off mode (e.g., hysteresis mode) isassociated with a third time period, T₃, 658, and an operational mode isassociated with a fourth time period, T₄, 660. Although the second timeperiod, T₂, 656, or the transitional excitation time period has twogenerally linear slopes (662, 664) in FIG. 6B, which are labeled firstslope m₁ (662) and second slope m₂ (664), the slope (662, 664) may becharacterized as single slope or a curved slope in alternateembodiments. The first slope represents rise or increase (e.g., firstrate of rise) in the direct current bus voltage over time in thetransitional excitation mode; the second slope represents a rise orincrease (e.g., second rate of rise) in the direct current bus voltageover time in the transitional excitation mode. For example, the directcurrent bus voltage increases a rate of a first slope between theprimary voltage level and the secondary voltage level, where the dataprocessor 128 can control (or is adapted to control, implement orachieve) the first slope by a first combination of commandedquadrature-axis current and a commanded direct-axis current of theelectric machine (e.g. in accordance with software instructions storedin the data storage device). Similarly, the data processor 128 cancontrol (or is adapted to control, implement or achieve) a directcurrent bus voltage that increases at a rate of the second slope betweenthe primary voltage level or an intermediate voltage level and thesecondary voltage level, where the intermediate voltage level is betweenthe primary voltage level and the secondary voltage (e.g. in accordancewith software instructions stored in the data storage device); the dataprocessor 128 controls, implements or achieves the second slope by thesecond combination of commanded quadrature-axis current and an commandeddirect-axis current (e.g., inflated commanded direct-axis current withrespect to the commanded direct axis current for the first slope) of theelectric machine.

As illustrated, a second slope, m₂, 664 may exceed the first slope, m₁,to reduce the total time or elapsed time from start-up mode during thefirst time period 654 (or inverter initialization or turn-on) to achievethe full operational target direct current voltage at the fourth timeperiod 660. The first slope m₁ 662 (e.g., lower slope) may be achievedby a first combination of commanded quadrature-axis current (e.g.,torque producing current) and a commanded direct-axis current (e.g.,field producing current) and the second slope m₂ 664 (e.g., greaterslope than the lower slope) may be achieved by the second combination ofcommanded quadrature-axis current (e.g., torque producing current) and acommanded direct-axis current (e.g., inflated commanded direct-axiscurrent or inflated field producing current). In one example, the dataprocessor 128 inflates the commanded direct-axis current of the secondcombination (e.g., by adjustment of the reference direct-axis currentvia a mathematical relationship or magnetic curve look-up table 118 orotherwise) with respect to the commanded quadrature-axis current of thefirst combination. In another example, for the first slope, the secondslope or both, a second current regulator 124 or data processor 128determines a commanded direct-axis (d-axis) voltage (V_(d)) based on ameasured d-axis current (I_(d) ^(measured)) and a determined or adjusted(e.g., inflated) d-axis reference current (I_(d) ^(ref)) derived from amathematical relationship between d-axis residual voltage (V_(d)^(residual)), the observed direct current bus voltage (V_(DC)^(measured)) and the commanded q-axis voltage (V_(q)) in which residualvoltage is proportional to a mathematical function of the measured,observed direct current voltage (V_(DC) ^(measured)) and the commandedq-axis voltage (V_(q)). In another example, the mathematicalrelationship is defined by a magnetic curve look-up table 118 thatcharacterizes the electric machine or induction machine.

The inflation of the commanded direct-axis current or voltage may reducethe time period, T₂ (656), of the transitional excitation mode such thatthe operational mode (e.g., T₄) is time-shifted to begin rapidly with anaccompanying reduction in the time period T₂ (656) of the transitionalexcitation mode; hence, any applicable load 300 can be connected orenergized in a responsive, real-time manner to the direct current bus ofthe inverter system, such as for hybrid vehicle operation whereresponsive acceleration or torque is required from an active load 300 ofa motor 302 connected to the direct current bus (28, 30).

In FIG. 6B, although the start-up mode is characterized by the directcurrent voltage across the capacitor 26 or direct current bus increasingrapidly followed by a knee or plateau at a an initial start-up voltage(level), a preliminary voltage, or initial voltage level 665 (e.g., V¹_(DC)) 665; the data processor 128, the data processing system 100, orthe trickle charging of one or more power supplies (22, 24, 12, 124,222, 224) may facilitate other curved or substantially linear increasesin the direct current voltage.

During the third time period, the hand-off mode (e.g., hysteresis mode)is characterized by a hand-off voltage (e.g., hysteresis voltage) or setstop voltage 667 (e.g., at V² _(DC)) in which the data processor 128 ordata processing system 100 monitors whether or not the direct currentvoltage bus exceeds the set stop voltage over one or more samplingintervals by a minimum voltage tolerance (e.g., 10 volts). In oneembodiment, the target operation voltage may equal the set stop voltageplus the minimum voltage tolerance. If during the third time period T₃(658) or the hand-off mode (e.g., hysteresis mode), the data processor128 or data processing system 100 determines that the direct currentvoltage bus exceeds the set stop voltage over one or more samplingperiods by a minimum voltage tolerance (or equals or exceeds the targetdirect current voltage), the data processor 128 or data processingsystem 100 switches to an operational mode, in which normal control ofthe induction machine 55 is commanded, such as voltage proportionalintegral control. For example, during the fourth time period T₄ (660) orin the operational mode, the data processor 128 may command or instructthe commanded direct-axis current and the commanded quadrature-axiscurrent consistent with operation with a rated magnetizing current ifthe rotor of the induction machine 55 is below the baseline speed orwith field weakening magnetizing current if the rotor of the inductionmachine 55 is above the baseline speed.

FIG. 7 is a block diagram that illustrates one possible configuration ofthe driver controller, the driver module 614, the inverter 311, theinduction machine 55 and the prime mover 201, such as an internalcombustion engine. Like reference numbers in FIG. 7 and any of the otherdrawings indicate like elements.

FIG. 7 shows one possible configuration of the driver module 614 thatcomprises a first phase driver 18, a second phase driver 118, and athird phase driver 218, consistent with FIG. 2. The electronic dataprocessing system 100, such as that illustrated in FIG. 5A, can be usedto control the driver module 614. The prime mover 201 or internalcombustion engine provides rotational energy to the induction machine 55by a coupling shaft 200. The induction machine 55 or generator convertsthe rotational energy into electrical energy in the operational modeafter the start-up mode (e.g., weak pre-charge mode) in which thecapacitor 26 across the direct current bus (28, 30) is trickle-chargedto provide a start-up voltage sufficient to energize one or morewindings of the induction machine 55. As illustrated the inductionmachine 55 comprises a squirrel cage induction machine 55, although anyother suitable induction machine may be used. The inverter 311 isanalogous to the inverter of FIG. 2, except that the switches (12, 112,212, 14, 114, 214) are illustrated schematically as metal oxide fieldeffect transistors.

FIG. 8 is one embodiment of a flow chart of a method for a self-excitingof an induction machine 55. The method of FIG. 8 begins in step S800.

In step S800, a voltage sensor 575 or inverter system (e.g., 11, 111,211, 311) measures an observed voltage across the direct current voltageterminals (28, 30) (e.g., direct current (DC) bus).

In step S802, a voltage difference module 104, a summer, or dataprocessor 128 determines a voltage difference (e.g., voltage bus error)between the observed voltage (from the voltage sensor 575) and areference DC bus voltage.

In step S804, a first current regulator 110 or data processor 128outputs a quadrature-axis (q-axis) voltage command (V_(q)) based on anelectrical current difference derived from the voltage difference. Forexample, the electrical current difference is derived from the voltagedifference between the measured, observed voltage (V_(DC) ^(measured))and a reference DC bus voltage (V_(DC) ^(ref)), where a controller 106(e.g., proportional integral controller) determines a quadraturereference current (I_(q) ^(ref)) from the voltage difference and where acurrent difference module 108 determines a difference (e.g., electricalcurrent difference or q-axis current error) between a quadraturereference current (I_(q) ^(ref)) and a measured, observed quadraturecurrent

(I_(q) ^(measured)) (e.g., measured q-axis command current) facilitatedby current measurements of one or more current sensors 577 for input tothe first current regulator 110. For example, a current sensor 577 canmeasure one or more phase currents that relate to a q-axis current(I_(q) ^(measured)). In one embodiment, a current sensor 577 is coupledto a data port 101; the current sensor 577 facilitates the provision ofa measured q-axis current to the electronic data processing system 100.For example, one or more current sensors 577 measure current for eachphase, such as I_(a), I_(b), and I_(c), where the inputs of a Parkstransformation module 615 is coupled to an output of each current sensor577 such that the Parks transformation module 615 transforms themeasured currents into a measured q-axis current, or into a measuredq-axis current (I_(q) ^(measured)) and a measured d-axis current. In oneembodiment of step S804, during the start-up mode, the controller 106,data processor 128, or proportional integral controller limits themagnitude of the change in signal amplitude over time in the quadraturereference current (I_(q) ^(ref)) such that the capacitor (C_(DC)) 26between the direct current voltage terminals (28, 30) has sufficienttime to charge and store adequate electrical energy or to reach acritical direct current voltage level, such as a start-up voltage orprimary voltage (e.g., a primary voltage level of approximately 20 VDCor greater) that can enable operation of the switches of the invertersystem 111 or primary inverter. In one embodiment, the data processor128 or proportional integral controller 106 may wait until the tricklecharge of the capacitor 26 or the direct current bus is substantiallycomplete or achieved the critical direct current voltage level beforeincreasing the quadrature reference current (I_(q) ^(ref). For example,in one embodiment the controller 106 or data processor 128 may model theestimated charging time of the capacitor 26 to wait for a minimum timeperiod to achieve the start-up voltage level prior to allowing amaterial or substantial increase in the in a quadrature referencecurrent (I_(q) ^(ref)) that is associated with a transition to theoperational mode (e.g., electrical generation mode of the inductionmachine 55) of the inverter from the start-up mode (e.g., charging ofthe capacitor).

In step S806, a second current regulator 124 or data processor 128determines a commanded direct-axis (d-axis) voltage (V_(d)) based on ameasured d-axis current (I_(d) ^(measured)) and a determined d-axisreference current (I_(d) ^(ref)) derived from a mathematicalrelationship between d-axis residual voltage (V_(d) ^(residual)), theobserved voltage (V_(DC) ^(measured)) and the commanded q-axis voltage(V_(q)) in which residual voltage is proportional to a mathematicalfunction of the measured, observed voltage (V_(DC) ^(measured)) and thecommanded q-axis voltage (V_(q)). In one embodiment, the start-up modeencompasses weak pre-charging of the capacitor 26 or the direct currentbus (e.g., defined by terminals 28, 30); once the pre-charging of thecapacitor 26 or direct current bus is complete, the data processingsystem 100 can initiate the excitation scheme that activates thetransitional excitation mode in which the excitation or self-excitationof the inverter system (111) or primary inverter occurs and the DC linkvoltage ramps up to the target operational direct current voltage inaccordance with step S806. Both the start-up mode and the transitionalexcitation mode occur prior to the full operational mode, although insome sense the transitional excitation mode or excitation stage relatesto start-up of the inverter prior to full operational switchingcapability because the available DC link voltage may be lower than atarget voltage.

Step S806 may be carried out in accordance with various techniques,which may be applied separately or cumulatively in a combination orpermutation for the start-up mode, the transitional excitation mode orboth.

Under a first technique, in the start-upstage, the transitionalexcitation mode, or both the electronic data processing system 100, thedata processor 128 or the second current regulator 124 selects commandedd-axis voltage (V_(d)) to provide or build up a higher DC link voltage(e.g., start-up direct current voltage or target direct current voltage)on the direct current terminals (e.g., direct current bus, 28, 30) forself-excitation for a corresponding commanded d-axis current thanotherwise required during the operational mode (e.g., for a given torqueand respective rotor speed or torque versus rotor speed for theinduction machine 55), consistent with the mathematical relationship,for enhanced (e.g., reliable and consistent) self-excitation of one ormore windings of the induction machine 55 or induction generator.

Under a second technique, during the start-up stage, the transitionalexcitation mode or both, the electronic data processing system 100, thedata processor 128 or the second current regulator 124 determines ad-axis residual voltage (V_(d) ^(residual)) in accordance with thefollowing equation (to fully use the DC bus and make the self-excitationof the windings of the induction machine robust consistent with rampingup the DC link voltage to a start-up direct current voltage or a targetdirect current voltage):

${V_{d}^{residual} = \sqrt{\frac{\left( {mV}_{DC}^{measured} \right)^{2}}{3} - V_{q}^{2}}};$where:

-   -   V_(d) ^(residual) is the residual direct-axis voltage;    -   m is the modulation index;    -   V_(DC) ^(measured) is the measured voltage of or between the        direct current terminals; and    -   V_(q) is the quadrature-axis voltage command. In one example,        the modulation index has a value within a range of zero to        approximately one. In another other example, the modulation        index is within a range of approximately 0.9 to approximately        0.95.

Under a third technique, in the transitional excitation mode the dataprocessor 128 or electronic data processing system 100 uses the d-axisresidual voltage (V_(d) ^(residual)) to inflate the reference d-axiscurrent command (I_(d) ^(ref)) above its normal value (e.g., based oncontrol look-up tables or characteristic data for particularcorresponding induction machines) for the reference d-axis currentcommand for the respective performance characteristics or specificationsof the particular induction machine 55 or induction generator. In turn,the inflated reference d-axis current command (I_(d) ^(ref)) causes agreater difference (e.g., error) between the measured d-axis current(I_(d) ^(measured)) and the inflated d-axis reference current (I_(d)^(ref)) as input to the second current regulator 124 that outputs thecommanded d-axis current consistent with ramping up the DC link voltageto a start-up direct current voltage or a target direct current voltage.The data processor 128 is adapted to or programmed with softwareinstructions to inflate a commanded direct-axis current via a magneticcurve look-up table (118) of a corresponding induction machine (55) withrespect to the commanded quadrature-axis current to reduce a time periodof a transitional excitation mode such that an operational mode istime-shifted to begin rapidly with an accompanying reduction in the timeperiod of transitional excitation mode. Accordingly, the third techniquecan reduce the duration of the transitional excitation mode to enhanceresponsiveness (e.g., available torque and acceleration response) of ahybrid vehicle, where the load 300 on the direct current bus (28, 30)comprises a motor 302 of a vehicle.

Under a fourth technique, after the start-up mode, during the start-upstage, or during the transitional excitation mode the electronic dataprocessing system 100 or the data processor 128 selects the direct-axisvoltage command to be equal to or greater than a threshold directcurrent link voltage (e.g., target start-up direct current voltage) ofor between the direct current terminals. For example, after the start-upmode or during the transitional excitation mode the threshold directcurrent link voltage may be within a range of approximately thirty voltsdirect current to approximately one hundred and fifty volts directcurrent, where approximately means about, generally or a margin ortolerance of plus or minus ten percent. However, after the start-upmode, after the transitional excitation mode, and during the normaloperational mode of the inverter, the electronic data processing system100 and data processor 128 transitions to or uses normal voltage andmodulation index control (e.g., for pulse width switching) of theinverter switches.

Under a fifth technique, the data processor 128 or electronic dataprocessing system 100 supports setting or storing of a transition directcurrent voltage level or start-up voltage level (e.g., direct currentlink voltage) of the observed direct current voltage to transitionbetween the start-up mode and the operational mode, or to transitionfrom the transitional excitation mode to the operational mode. Forinstance, the transition direct current voltage level, start-up voltagelevel, and the target direct current voltage may comprise a factoryprogrammable, user-definable, or otherwise programmable values. Theinverter begins at transitional excitation mode or excitation stage oncethe start-up voltage level of the direct current bus is reached (e.g.,at the end of T₁). The inverter ends the transitional excitation mode(of T₂) or the excitation mode when the target direct current voltage ofthe direct current bus is achieved (at T₃ or T₄).

Under a sixth technique, the data processor 128 or electronic dataprocessing system 100 determines the d-axis reference current (I_(d)^(ref)) for a corresponding residual d-axis voltage (V_(d) ^(residual))based on a magnetizing curve or K-factor look-up table stored in a datastorage device 120. This d-axis reference current is determined bycharacterizing the induction machine 55 in the lab or field tests, byobtaining specifications from a manufacturer or designer of theinduction machine 55, or by other empirical or statistical studies of aset of particular induction machine 55s. An accurate magnetizing curvefor a corresponding induction machine 55 can be critical for successfulself-excitation starting from a very low start-up voltage on DC voltageterminals or DC bus terminals.

In step S808, a data processor 128 or an inverse Parks transformationmodule 612 provides phase voltage commands (V_(a), V_(b), V_(c)) basedon inverse Parks transform or a similar transformation of the commandedvoltages (V_(d) and V_(q)). For example, the data processor 128 orinverse Parks transformation module 612 may determine the Parkstransformation or a similar transformation in accordance with using theposition based on the following equation of the rotor field orientation:θ_(e)=θ_(rotor)+∫ω_(slip) dt,

where θ_(e) is the electrical angular position of the rotor;

where θ_(roto) is the mechanical angular position of the rotor;

and ω_(slip) is the angular slip velocity of the rotor.

The angular slip velocity of the rotor (ω_(slip)) is the controlvariable. The controller 106 or data processor 128 commands the correctoperation of the slip point of the angular slip velocity using d and qaxes current control. In particular, the reference d-axis current andthe reference q-axis current are critical in determining one or more ofthe following items: (1) correct slip point, (2) minimum slip value, (3)maximum slip value, (4) minimum slip value as a function of rotor speedof the induction machine 55, and (5) maximum slip value as a function ofrotor speed of the induction machine 55.

FIG. 9 is another embodiment of a flow chart of a method for aself-exciting of an induction machine 55. The method of FIG. 9 begins instep S800. Like reference numbers in FIG. 8 and FIG. 9 indicate likesteps, procedures or features.

In step S800, a voltage sensor 575 measures an observed voltage acrossthe direct current voltage terminals (28, 30) (e.g., DC bus).

In step S802, a voltage difference module 104, a summer or a dataprocessor 128 determines a voltage difference (e.g., voltage bus error)between the observed voltage and a reference DC bus voltage.

In step 910, a controller 106 or data processor 128 generates areference q-axis current command (I_(q) ^(ref)) based on the voltagedifference. For example, a proportional integral (PI) controller ascontroller 106 generates a reference q-axis current command (I_(q)^(ref)) based on the voltage difference.

In step S912, a current sensor 577 measures a q-axis current (I_(q)^(measured)). A current sensor 577 can measure one or more phasecurrents that relate to a q-axis current (I_(q) ^(measured)). In oneembodiment, one or more current sensors 577 facilitate the provision ofa measured q-axis current to the electronic data processing system 100.For example, one or more current sensors 577 measure current for eachphase, such as I_(a), I_(b), and I_(c), where the inputs of a Parkstransformation module 615 is coupled to an output of each current sensor577 such that the Parks transformation module 615 transforms themeasured currents into a measured q-axis current, or into a measuredq-axis current and a measured d-axis current. In step S914, a currentdifference module 108, a summer or a data processor 128 determines acurrent difference (e.g., q-axis current error) between the measuredq-axis command current and the reference q-axis current command (I_(q)^(ref)).

In step S804, a first current regulator 110 outputs a q-axis voltagecommand (V_(q)) based on an input of the current difference, such as thecurrent difference (e.g., q-axis current error) between the measuredq-axis command current and the reference q-axis current command (I_(q)^(ref)). For example, the first current regulator 110 outputs a q-axisvoltage command (V_(q)) based on an input of the current differencebased on a proportional integral control compensator or similar transferfunction, which may be represented as a separate block within the firstcurrent regulator 110. The first current regulator 110 outputs a q-axisvoltage command (or its equivalent q-axis current command) to theinverse Parks transformation module 612. The inverse Parkstransformation module 612 uses the q-axis voltage command, the d-axisvoltage command, and measured rotor position (e.g., electrical rotorposition, θ_(e), based on mechanical rotor position and slip anglevelocity) to provide appropriate control signals (e.g., commanded q-axisvoltage (V_(q)) for each phase) to the driver module 614.

In step S916, a data processor 128 determines a d-axis residual voltage(V_(d) ^(residual)) in accordance with the following equation (to fullyuse of the DC bus and to facilitate robust, reliable self-excitation ofthe windings of the induction machine):

${V_{d}^{residual} = \sqrt{\frac{\left( {mV}_{DC}^{measured} \right)^{2}}{3} - V_{q}^{2}}};$where

V_(d) ^(residual) is the residual direct-axis current;

m is the modulation index (e.g., approximately 0.95);

V_(DC) ^(measured) is the measured voltage of or between the directcurrent terminals; and

V_(q) is the quadrature-axis voltage command.

Step S916 may be carried out in accordance with various techniques thatmay be applied alternately or cumulatively in the start-up stage, in thetransitional excitation mode, or both.

Under a first technique, the data processor 128 or electronic dataprocessing system 100 uses the d-axis residual voltage (V_(d)^(residual)) to inflate the reference d-axis current command (I_(d)^(ref)) above its normal value for the reference d-axis current commandfor the respective performance characteristics of the particularinduction machine 55 or induction generator. In turn, the inflatedreference d-axis current command (I_(d) ^(ref)) causes a greaterdifference (e.g., error) between the measured d-axis current (I_(d)^(measured)) and the inflated d-axis reference current (I_(d) ^(ref)) asinput to the second current regulator 124 that outputs the commandedd-axis current consistent with ramping up the DC link voltage to astart-up direct current voltage or a target direct current voltage.

Under a second technique, during the start-up stage, after the start-upmode, or during the transitional excitation mode the electronic dataprocessing system 100 or the data processor 128 selects the direct-axisvoltage command to be equal to or greater than a threshold directcurrent link voltage (e.g., target start-up direct current voltage ortarget operational direct current voltage) of or between the directcurrent terminals. For example, during the start-up mode or during thetransitional excitation mode the threshold direct current link voltagemay be within a range of approximately thirty volts direct current toapproximately one hundred and fifty volts direct current, whereapproximately means about, generally or a margin or tolerance of plus orminus ten percent. However, after the start-up mode or after thetransitional excitation mode during the normal operational mode of theinverter, the electronic data processing system 100 and data processor128 transitions to or uses normal voltage and modulation index control(e.g., for pulse width switching) of the inverter switches.

Under a third technique, the data processor 128 or electronic dataprocessing system 100 supports setting or storing of a transition directcurrent voltage level or start-up voltage level (e.g., direct currentlink voltage) of the observed direct current voltage to transitionbetween the start-up mode and the operational mode, or to transitionfrom the transitional excitation mode to the operational mode. Forinstance, the transition direct current voltage level or start-upvoltage level and the target direct current voltage may comprise afactory programmable, user-definable, or otherwise programmable value.The inverter begins at transitional excitation mode once the start-upvoltage level of the direct current bus is reached. The inverter endsthe transitional excitation mode or the self-excitation mode when thetarget direct current voltage of the direct current bus is achieved oronce the optional hand-off mode is completed.

Under a fourth technique, the data processor 128 or electronic dataprocessing system 100 determines the d-axis reference current (I_(d)^(ref)) for a corresponding residual d-axis voltage (V_(d) ^(residual))based on a magnetizing curve or K-factor lookup table stored in a datastorage device 120. This d-axis reference current is determined bycharacterizing the induction machine 55 in the lab or field tests, byobtaining specifications from a manufacturer or designer of theinduction machine 55, or by other empirical or statistical studies of aset of particular induction machines 55. An accurate magnetizing curvefor a corresponding induction machine 55 can be critical for successfulself-excitation starting from a very low start-up voltage on DC voltageterminals or DC bus.

In step S918, the data processor 128 or data processing systemdetermines the d-axis reference current (I_(d) ^(ref)) for acorresponding residual d-axis voltage (V_(d) ^(residual)) based on amagnetizing curve or K-factor lookup table stored in a data storagedevice 120.

In step S920, a second current regulator 124 (e.g., complex vectorcurrent regulator) determines the commanded d-axis voltage (V_(d)) basedon the measured d-axis current (I_(d) ^(measured)) and the determinedd-axis reference current (I_(d) ^(ref)).

In step S808, a data processor 128 or an inverse Parks transformationmodule 612 provides phase voltage commands (V_(a), V_(b), V_(c)) basedon inverse parks transform or a similar transformation of the commandedvoltages (V_(d) and V_(q)). For example, the data processor 128 orinverse Parks transformation module 612 may determine the Parkstransformation or a similar transformation in accordance with thefollowing equation of the rotor field orientation:θ_(e)=θ_(rotor)+∫ω_(slip) dt,

where θ_(e) is the electrical angular position of the rotor;

where θ_(roto) is the mechanical angular position of the rotor;

and ω_(slip) is the angular slip velocity of the rotor.

The angular slip velocity of the rotor (ω_(slip)) is the controlvariable. The controller 106 or data processor 128 commands the correctoperation of the slip point of the angular slip velocity using d and qaxes current control. In particular, the reference d-axis current andthe reference q-axis current are critical in determining one or more ofthe following items: (1) correct slip point, (2) minimum slip value, (3)maximum slip value, (4) minimum slip value as a function of rotor speedof the induction machine 55, and (5) maximum slip value as a function ofrotor speed of the induction machine 55.

In accordance with the system and method in this document, one or morepower supplies (e.g., of compact or modest size, low or modest cost, andlow or modest current output) associated with the driver of the invertercan provide sufficient initial energy to charge a capacitor in astart-up mode. Because the power supplies only require a modest currentoutput to sufficiently trickle charge the capacitor during the start-upmode, the system and method are well suited for repurposing orleveraging ordinary or typical driver circuitry of the inverter tocharge the capacitor. Further, the capacitor that is charged may beembodied as a typical or existing capacitor that is already used acrossthe direct current bus for filtering (e.g., voltage transients) of thedirect current signal of the inverter.

To facilitate the proper use of the stored energy in the capacitoracross the terminals of the direct current bus, (e.g., in a transitionalexcitation mode) an electronic data processing system can controlswitches of the driver to control the power supplies of the driver tojudiciously and efficiently deploy the energy stored in the capacitorfor a successful transition to an operational mode from a start-up modeor start-up stage. The method and system facilitates efficientmanagement of the electromagnetic flux and generated current induced inthe induction machine after the start-up mode fully or adequatelycharges the capacitor to increase gradually the generated current thatcreates braking (generating) torque on a shaft that is rotated. Forexample, the electronic data processing system increases the inducedcurrent and voltage output of the induction machine in controlledincremental steps, in successive graduated steps, or in accordance witha continuous ramping process. In one embodiment, the data processingsystem sets the ramp-up rate of increase in electromagnetic flux andgenerated current or generated voltage in the induction machine to avoiddischarging the capacitor in a manner that interferes withself-excitation of the electrical energy in the induction machine toachieve an operational mode at a target voltage output on the directcurrent bus. Accordingly, the induction machine is capable of producingelectrical power which charges the capacitor, replaces the initialstored energy in the capacitor and increases the output voltage beyondthe level attainable by the power supplies or driver circuit alone.

Having described the preferred embodiment, it will become apparent thatvarious modifications can be made without departing from the scope ofthe invention as defined in the accompanying claims.

The following is claimed:
 1. An inverter system comprising: a pair ofdirect current voltage terminals of opposite polarity; a capacitorconnected between the direct current voltage terminals; a first switchhaving first switched terminals and a first control terminal; a secondswitch having second switched terminals and a second control terminal,the switched terminals of the first switch and the second switch coupledin series, between the direct current voltage terminals; an electricmachine or generator having one or more windings and a first phaseoutput terminal associated with the switched terminals between the firstswitch and the second switch; a first set of blocking diodes in series;a second set of blocking diodes in series; a first voltage supplyproviding a first output voltage level and a second output levelswitchable to the first control terminal, the first output leveldistinct from the second output level, the first output level providingelectrical energy via the first set of blocking diodes to the capacitorto charge or trickle charge the capacitor in a start-up mode to aprimary voltage level; a second voltage supply providing the firstoutput voltage level and the second output level switchable to thesecond control terminal, the first output level providing electricalenergy via the second set of blocking diodes to the capacitor to chargeto trickle charge the capacitor in the start-up mode to the primaryvoltage level; and in a transitional excitation mode, the electricmachine capable of inducing alternating current flux in one or morewindings associated with the first phase output terminal to ramp up avoltage level of the direct current voltage terminals from the primaryvoltage level to a secondary voltage level, where the secondary voltagelevel is associated with an operational mode of the inverter system. 2.The inverter system according to claim 1 wherein the primary voltagelevel is sufficient to enable operation of the first switch and thesecond switch consistent with the induction or excitation of alternatingcurrent flux in the one or more windings.
 3. The inverter systemaccording to claim 1 further comprising: during a time period associatedwith the transitional excitation mode, a data processor for controllinga first slope of the direct current bus voltage by a first combinationof commanded quadrature-axis current and a commanded direct-axis currentof the electric machine, where the direct current bus voltage increasesat a rate of the first slope between the primary voltage level and thesecondary voltage.
 4. The inverter system according to claim 3 whereinduring a time period associated with the transitional excitation mode,the direct current bus voltage increases at a rate of the first slopeand a rate of a second slope between an intermediate voltage level andthe secondary voltage level, the second slope being greater than thefirst slope, wherein that data processor is adapted to control the firstslope by a first combination of commanded quadrature-axis current and acommanded direct-axis current of the electric machine and the dataprocessor is adapted to control the second slope by a second combinationof quadrature-axis current and an inflated commanded direct axis currentadjusted based on a mathematical relationship.
 5. The inverter systemaccording to claim 4 wherein the mathematical relationship is betweend-axis residual voltage, the observed direct current bus voltage and thecommanded q-axis voltage in which residual voltage is proportional to amathematical function of the measured, observed direct current busvoltage and the commanded q-axis voltage.
 6. The inverter systemaccording to claim 1 wherein the first voltage supply is associated witha first control switch between the first control terminal the firstoutput voltage level and a second control switch between the firstcontrol terminal and the second output level.
 7. The inverter systemaccording to claim 6 wherein the first control switch is off, orinactive, during the start-up mode and wherein the first control switchalternates between off and on during an operational mode in accordancewith modulation commands after the transitional excitation mode orcompletion of self-excitation of the of alternating current flux in oneor more windings associated with the first phase output terminal.
 8. Theinverter system according to claim 6 wherein the second control switchis on, or inactive, during the start-up mode and wherein the secondcontrol switch alternates between on and off, during the operationalmode.
 9. The inverter system according to claim 1 wherein the firstoutput voltage level is greater than the second output level, andwherein at the primary voltage level the capacitor is charged to twicethe first voltage level, less a first voltage drop associated with thefirst set of diodes and a first resistor in series with the first set ofdiodes and less a second voltage drop associated with the second set ofdiodes and a second resistor in series with the second set of diodes.10. The inverter system according to claim 1 further comprising anelectrical direct current load or battery coupled between the directcurrent terminals during the operational mode and after the start-upmode.
 11. The inverter system according to claim 1 wherein theelectrical direct current load or battery is coupled to the directcurrent terminals via a load switch that is off during the start-up modeand on during an operational mode.
 12. The inverter system according toclaim 1 further comprising: a third switch having third switchedterminals and a third control terminal; a fourth switch having fourthswitched terminals and a fourth control terminal, the switched terminalsof the third switch and the fourth switch coupled in series, between thedirect current voltage terminals; a second phase output terminalassociated with the switched terminals between the third switch and thefourth switch; a third set of blocking diodes in series; a fourth set ofblocking diodes in series; a third voltage supply providing a firstoutput voltage level and a second output level switchable to the thirdcontrol terminal, the first output level providing electrical energy viathe third set of blocking diodes to the capacitor to charge or tricklecharge the capacitor in a start-up mode to a primary voltage level; in atransitional excitation mode, the electric machine inducing alternatingcurrent flux in one or more windings associated with the second phaseoutput terminal to ramp up or increase a voltage level of the directcurrent voltage terminals from a primary voltage level to a secondaryvoltage level; and a fourth voltage supply providing the first outputvoltage level and the second output level switchable to the fourthcontrol terminal, the first output level providing electrical energy viathe fourth set of blocking diodes to the capacitor to charge or tricklecharge the capacitor in a start-up mode to the primary voltage level;and in the transitional excitation mode, the electric machine inducingalternating current flux in one or more windings associated with thefirst phase output terminal to ramp up a voltage level of the directcurrent voltage terminals from the primary voltage level to a secondaryvoltage level.
 13. The inverter system according to claim 12 where thefirst phase output terminal and the second phase output terminal areconnected in parallel to the windings to enhance collectively the outputpower capacity of the first voltage supply, the second voltage supply,the third voltage supply and the fourth voltage supply to aid in theself-excitation of an induction machine.
 14. The inverter systemaccording to claim 12 wherein the first output level provides electricalenergy via the third set of blocking diodes and via the fourth set ofblocking to the capacitor to charge or trickle charge the capacitor toachieve the start-up voltage level to start the self-excitation ofalternating current flux in one or more windings associated with thesecond phase output terminal.
 15. The inverter system according to claim1 wherein: a secondary inverter comprising a plurality of direct currentinput terminals and alternating current output terminals, the pair ofdirect current voltage terminals coupled to the direct current inputterminals; an electric motor coupled to the alternating current outputterminals, the secondary inverter adapted to control the electric motorthrough signals provided at the alternating current output terminals.16. The inverter system according to claim 15 wherein the secondaryinverter and the electric motor comprise an active load on thegenerator.
 17. The inverter system according to claim 1 wherein thegenerator comprises an induction machine without any energy storagedevice connected between the direct current voltage terminals, exceptfor the capacitor, and without any capacitor connected to the firstphase output terminal.
 18. The inverter system according to claim 17wherein the induction machine does not include any permanent magnets inor for the rotor.
 19. The inverter system according to claim 1 whereinthe generator generates an operational voltage level exceedingapproximately six hundred (600) volts during the operational mode afterthe capacitor is trickle charged during the start-up mode to a start-upvoltage level that exceeds approximately fifteen (15) volts.
 20. Theinverter system according to claim 1 wherein after charging thecapacitor, a driver is adapted to apply the first output level to theactivate the first switch, whereas the second level is applied todeactivate the first switch in accordance with a pulse width modulationcommands.
 21. The inverter system according to claim 1 wherein the firstoutput level provides electrical energy via the first set of blockingdiodes and via the second set of blocking to the capacitor to charge ortrickle charge the capacitor to achieve the start-up voltage level tostart the self-excitation of alternating current flux in one or morewindings associated with the first phase output terminal.
 22. Theinverter system according to claim 1 further comprising: a dataprocessor for inflating a commanded direct-axis current via a magneticcurve look-up table of an induction machine with respect to thecommanded quadrature-axis current to reduce a time period of thetransitional excitation mode.
 23. The inverter system according to claim22 wherein the data processor is adapted to inflate the residualdirect-axis current to increase the robustness of an excitation processof the electromagnetic field in the one or more windings and theassociated increase in direct current voltage.
 24. The inverter systemaccording to claim 1 further comprising: a data processor is adapted todetermine that an excitation stage is complete and has reached thesecondary voltage level of the target operational direct current voltageby a hysteresis algorithm or by a timer that is triggered when thetarget operational direct current voltage meets or exceeds a thresholdvoltage for at least a minimum time period.